Zombies, Dragons and Eunuchs: The Science behind Game of Thrones

September 24, 2017
10 min
How hot is Drogon's fire? Where did the walking dead come from? What disease inspired greyscale? And where can you find dragonglass? A few scientific questions that arose during the seventh season of Game of Thrones

The seventh season of Game of Thrones came to an end, and it will be a year and a half before we shall see winter in Westeros once again. To ease our anticipation, here are some scientific thoughts on what we saw this past season.

The walking dead

During the last season, we felt the threat of the walking dead from the north more than ever. We had the opportunity to see them fight, kill, and even die. The zombies on Game of Thrones seem very different than those we are used to seeing on screens, from The Night of the Living Dead to The Walking Dead. They do not eat brains or corpses; head amputation or a knife to the brain do not stop them; they do not transmit “the disease” to anyone they bite; and they are completely controlled by the White Walkers (or “the Others”), who created them – to such a degree that they die when their White Walker dies.

One may claim that they are not zombies at all, and indeed, both in the books and in the series, they are called “wights.” However, if we look into the source of the belief in living-dead, we would discover that the original zombies resembled George Martin’s version more than those of George Romero.

Zombies first appeared as part of voodoo religion in Haiti in the 18th century. According to the belief, voodoo sorcerers can breathe life into the dead, but before doing so, they trap the spirit of the dead person in a jar or container. The resurrected person cannot speak, has no memory, and is easy to control. Sorcerers may use these zombies for agricultural or construction work. They are not considered particularly dangerous, and definitely not contagious. In addition, letting them eat salt would bring back their memory and ability to speak. When the sorcerer dies, the zombies return to their village or burial site and die (remind you of anything?).  

Over the years, there were supposedly some cases of people that returned to their village, years after their death and burial. It was claimed that during the entire time, they served a sorcerer as zombies. It is plausible that most, if not all, of these people were frauds, trying to impersonate someone else, but some researchers think there might be a scientific explanation to the zombies from Haiti.

Wade Davis proposed that it was not that the sorcerers were bringing people back to life; but that they make living people seem dead. He claims they do this using tetrodotoxin, the toxin of the Fugu fish. Davis even found traces of this toxin in powders found in the sorcerers’ possession. When this powder is administered, the victims become paralyzed, their heartrate slows down, and they appear dead; but a few hours later, with or without the assistance of the sorcerer, they recover and “return to life.” The sorcerer then gives them other drugs, possibly containing Datura, which then impair their consciousness for the rest of their lives as “zombies”.

Not everyone accepts Davis’s claims. Some researchers doubt that the poison can actually induce a death-like state that can be recovered from, and especially that all voodoo sorcerers can administer the exact dosage for this to happen.  

Of course, the White Walkers of Westeros do not need powders and drugs – they wake the dead without even touching them. Their zombies are also much more aggressive than those of Haiti, and it is much more difficult to kill them. Their other characteristics, however, are quite similar.


The wights of Game of Thrones | Screenshot from episode six, season seven, HBO

Breaths of ice and fire?

The dragons’ breath of fire on Game of Thrones, which are actually fire-breathing wyverns, or at least that of Drogon, according to the fourth and fifth episodes of the seventh season, is capable of burning a person to ashes. To fully incinerate a body, including the bones, as it seems Drogon does, a very high temperature is required. A lower temperature would be sufficient if it weren’t for the bones.

Crematories that are used for burning bodies reach temperatures of up to 980 degrees Celsius. The organic materials and water inside the body evaporate, leaving behind not dust, but dry and broken bones. The remains of the bones are crushed to dust using an electric or manual machine after cremation. To skip the crushing process and have the bones disintegrate without it, it would be worthwhile to try and melt them. The melting temperature of hydroxyapatite, which makes up about 70% of bone tissue, is 1,670ºC – but this temperature may not suffice to melt down bone, which is not comprised only of pure hydroxyapatite. It is more plausible that Drogon burned and weakened the bones, which disintegrated upon impact – from the fall and from the armor parts falling on them – rather than actually burning them to ashes.

Burning bodies in the crematory takes about two hours, but in the series, people were burnt in seconds. The process is probably accelerated due to the large amount of fire in one dragon breath and due the fast flow of hot air.

According to Westeros stories, the breath of fire of Balerion, Aegon the Conqueror’s huge black dragon, melted down the walls of the castle of Harrenhal. Assuming the castle walls were made of granite stone, like many castles throughout England, their melting temperature would be around 1,250ºC. If they were constructed from something even more durable, such as rocks containing aluminum oxide, the melting temperature would be even higher, reaching about 2,050ºC. However, Daenerys’s dragons are smaller than Balerion. They can neither melt walls or chains made of iron (1,510ºC) nor steel (about 1,370ºC, depending on the oxygen content). At best, they would be able to weaken the chains, for which only a relatively low temperature, of about 540ºC will do.

Viserion’s death on episode six reveals a part of the fire-breathing mechanism in the world of Game of Thrones, and may help estimate the temperature of their breath. When the Night King, which might be Brandon Stark according to the books, throws his ice spear and pierces Viserion’s body, some form of flammable gas seems to come gushing out of the wound at the bottom of his neck and above his wing. The gas ignites and explodes, causing the dragon to plummet to his death. It is plausible that the source of the gas is in the sack at the bottom of the dragon’s neck. The sack probably stores flammable gases produced by the dragon’s body under high pressure. This resembles flammable gases, such as methane, which are produced by bacteria in the digestive systems of humans and other animal.

Drogon’s flame, like the other dragons, is yellow-orange. If this flame is indeed produced by a carbon-based gas burning in the air, this color is compatible with a temperature of about 1,200ºC, which is consistent with the state in which the dragon breath left the burned bodies and armors. Balerion’s abilities show that this temperature rises as the dragons grow larger, unless the breath of fire is replaced by a different power, in the event that Drogon and Rhaegal join their undead brother.


The injury leads to an explosion, probably of flammable gas. The death of Viserion the dragon | Short sequence from episode six, season seven, HBO

In the final episode’s last scene, the undead Viserion manages to knock down a part of the large ice wall in the north of Westeros. The wall was built by another Brandon Stark – Bran the Builder – out of steel, dirt, and mostly ice. The giants assisted in its construction and the children of the forest, who cast strong water spells, reinforced the wall. The mean height of the wall is 213 meters, and it is 480 kilometers long and 90 meters wide. Without the spell, such a structure would collapse since it would have to face some annoying laws of physics. In addition, the spells of the children of the forest prevent, or rather, had prevented, the undead, such as the wights and the White Walkers (the Others) from crossing the wall.

When undead Viserion, whose breath is a blue fire-like force, concentrates his breath on one point, he is able to blow a hole in the wall. How much energy does this actually require?

We asked Dr. Noa Lachman, a materials expert from Tel Aviv University, to help us estimate the force and power of the dragon’s breath.

Before we begin our calculation, we need a little bit of information. The thickness of the wall Viserion blew through is 90 meters. We will regard the entire wall as comprised from pure ice, so a pressure of 25 million pascals, or 25 million newtons per square meter, is required to break it.

What is the volume that was broken in? Since we know the height of the wall, we can calculate the diameter of the part of Viserion’s breath that hit the wall, as can be observed in the following screenshot.
The diameter of the dragon's breath compared to the height of the wall | Screenshot from episode seven, season seven, HBO

According to this calculation, the diameter is 3.15 meters and the volume of the initial “hole” – the cylinder that is smashed in – is π times 1.575 (half the diameter) squared, times 90 (the thickness of the wall), which results in 701 square meters.

The energy required for breaking in a volume like this is 17,525 million newton meters (701 times 25 million) or 17,525 million joules. This energy is equivalent to that produced by an explosion of 4.2 tons of TNT.

Viserion released all of this energy in 34 seconds, making the power of his breath about 515 million joules per second, or 515 megawatts. In more familiar units, this is equivalent to about 691 horsepower (or one “dragon-breath power”).  

Dragonglass from the heart of the Earth

“Obsidian. Forged in the fires of the gods, far below the earth. The children of the forest hunted with that, thousands of years ago. The children worked no metal... In place of swords, they carried blades of obsidian.” – Maester Luwin, Game of Thrones.

In our world, obsidian is a sort of volcanic glass, which forms when lava from volcanos cools down quickly. One could say Maester Luwin was right: the fire that creates this kind of glass is under the ground, in the house of the god Vulcan.

In contrast, the children of the forest say that the “dragonglass” is forged in the fire of dragons. The giant rock made of obsidian under Dragonstone is a strong piece of evidence to support that claim. But is the fire of dragons strong enough?

Obsidian forms when lava contains a high percentage of silicon dioxide, the main ingredient in sand. These rocks melt at a relatively low temperature, less than 900ºC. Dragons, as we mentioned earlier, are able to reach such temperatures. We do not know if the glass at Dragonstone was indeed created by dragons (perhaps only Bran could know this), but it seems to be feasible, as long as they can blow fire for a long enough time.

The color of obsidian is usually black and it is strong and fragile, with very sharp edges after breaking – much sharper than metal knives. For this reason, it was also used in the real world to make hunting and cutting tools in cultures that existed before the Iron Age. Early Homo species made obsidian knives as early as 1.4 million years ago, and tools made by our species, Homo Sapiens, have been discovered anywhere from Africa to America. In Israel, obsidian tools thousands of years old were found next to the town of Gilat in the northern Negev area. The glass most likely originated in Turkey; finding it in Gilat indicates that wide-scale commerce took place, and also attests to the importance of this material to the people of the region, who bothered to import it from afar.

For obvious reasons, we have no way of knowing whether the tools found in our world have magical powers that enable them to kill White Walkers and wights. But even without superpowers, their physical properties were sufficient to render them very special for the people of the Stone Age.

Arrowhead made from obsidian | Shutterstock  

50 scales of grey

Greyscale is a contagious disease and seems to be revolting to the people in the world of Game of Thrones. In a previous article we wrote about it, we mentioned that it is incurable – but in the last season, Samwell Tarly demonstrated that it is not so by curing Jorah Mormont.

The disease is transmitted easily from person to person via skin contact, and can even be transmitted from contaminated animals or objects, like the doll that transmitted the disease to the unlucky princess Shireen Baratheon. Following infection, the disease slowly spreads throughout the body. In the beginning, the only sign is numbness at the infection site, which then spreads to other areas of the body. Then the afflicted skin hardens and cracks like dry soil and, at more advanced stages, the skin becomes very thick and stiff, turning grey or black. The skin closely resembles grey scales of reptiles, which is where the disease name came from. Puss accumulates under the scales, indicating the (failing) battle of the body against the greyscale.

If the scales reach the facial area, they may lead to blindness. The final and most awful stage of disease occurs many years after the infected individuals have become “stone men,” covered in scales from top to bottom. At this stage, the disease attacks the internal systems – the bones, muscles, nervous system, etc. Those who survive up to this stage will lose their minds and often become violent.  

Children that contract greyscale may recover, however rarely, leaving only a remnant scar. These children then become immune to the disease and to its much more violent relative “grey death.” Nevertheless, many times they are executed, in fear they will transmit the disease to others. For most people, who were not exposed to the books that Sam has read, the only way to deal with the disease is through prevention. As there are no vaccines in Game of Thrones, prevention is achieved by enclosing infected areas and killing whoever tries to leave, or by sending the infected individuals to distant “leper colonies.”  

Thankfully, in the real world, no disease exists with all of the properties of greyscale, but there are several similar diseases. Leprosy (Hansen’s disease), for instance, begins as a skin lesion, and later on develops into various skin growths and peripheral nerve damage that may impair sensation, motion, and vision. At advanced stages, the limbs and nose become deformed, along with some other unpleasant phenomena. In addition, lepers were segregated from society, like those infected with greyscale. Leprosy may have inspired George R. R. Martin's greyscale, but in contrast to it, leprosy is barely contagious. 

In the previous article, we mentioned other diseases. For instance, smallpox is a very contagious and deadly disease that can be transmitted through breathing or contaminated objects and leads to many lesions covering the skin. The human papilloma virus (HPV) is another example for a virus that is easily transmitted via skin contact and leads to skin lesions, as well as cancer, in certain strains.

However, neither smallpox, papilloma, nor even leprosy explain the brain damage that occurs at the final stages of greyscale. A better fit, exhibiting both skin lesions and brain damage, is syphilis. This is an extremely contagious and dangerous disease that is transmitted via skin contact, mostly during sexual intercourse or by sharing sex toys, but can also be transmitted through blood and saliva, or even close contact with an afflicted area in the body. At the first stage of syphilis, only a skin lesion appears. The second stage, occurring about two months following infection, a rash appears, as well as small warts on the genitals, joint pain, local hair loss, etc. The third stage of syphilis breaks out only many years later. At this stage, the body of the infected individual gradually disintegrates – the nose sometimes falls off, walking becomes a problem, blindness may develop, and as their body deforms and fades away, patients will lose their sanity.  

Therefore, greyscale is an imaginary disease incorporating leprosy, syphilis, and perhaps additional real-life diseases, which is also much more contagious and deadly than either of them.

Both syphilis and leprosy can be treated with antibiotics, but if nerve damage occurs, as well as damage to other organs, it will persevere even after successful treatment. In the world of Game of Thrones there are no antibiotics, and the ointment that Sam Tarly applied on Jorah does not have very promising medical properties: It is composed of pine resin, green bark of elder twigs, white beeswax, and olive oil. Therefore it seems that Jorah’s recovery happened mainly due to Sam treating him with an especially deep-tissue peel.

How is this possible? We can only guess. Perhaps as long as the disease has not spread to internal organs, it is enough to simply remove every afflicted piece of skin – like removing a wart – in order to cure the disease, even if it leaves scars. This is probably the reason why amputation of an afflicted organ may halt the greyscale before it spreads on top of the skin – the unknown disease-causing agent spreads near the surface and not inside the body, at least not at first. In addition, the puss that was apparent during the peeling process indicates immune system activation. It may be possible that removal of most of the afflicted and infested areas has allowed Jorah’s immune system to finally overcome the disease.   


Sam treating Jorah's disease | Screenshot from episode two, season seven, HBO

The perks of being a eunuch

Theon Greyjoy may not be an incredibly skilled or strong warrior, but he has a secret weapon: He is fully resistant to the greatest fear of any other man around – getting hit in the groin. We know Theon lost his penis while being tortured by Ramsay, and according to the battle he fought in the last episode, we are also pretty certain he also lacks testicles. But, is a eunuch without a penis or testicles really resistant to a blow below the belt?

Most of the pain from a kick to the groin indeed comes from the testicles themselves. The scrotum contains many nerve cells that transmit pain to the brain. Since the testicles are not protected by bone, muscle or a thick layer of fat, it is pretty easy to activate these nerve cells.

In addition, a blow to this area leads to referred pain, i.e., not only does the area itself ache, but also the abdomen and sometimes more distant areas. The source of the referred pain is usually not in the nerve cells inside the skin, but in more internal cells, in this case, inside the penis and testicles. A strong-enough blow also activates these internal nerve cells, causing pain in vast areas of the body.

This means that lacking external genitals would indeed reduce the pain of the receiver of a kick to that area. Reduce, but not completely prevent, of course – a kick is still a kick, and there are also nerve cells in the pelvis, not to mention a wound that may have remained after the not-so-medical procedure. Therefore, we are not certain if even someone with no genitals could actually stand and smile at the attacker like Theon did, but maybe he is tougher than he looks. If it will help him save Yara, we are definitely for it.

Translated by Elee Shimshoni