Season 1: Episode 5- Trolls (Trollhunter- 2011)

We get stuck into the trolls from 2011’s cult classic Troll Hunter. Dave decides that the real monsters are the people, Dave accuses all vets of drug use, and Dave just loses his goddamn mind. This one’s pretty Dave heavy. He deserves it.

5:31 – Movie History
17:27 – Movie Any Good?
19:11 – Physiology of the Trolls
51:34 – Ecology of the Trolls
1:12:55 – The Troll Hunter vs. Bear Grylls

Film: Trollhunter [2010]
Production Company: Filmkameratene A/S & Film Fund FUZZ
Distribution By: SF Norge A/S
Monster: Trolls
Featuring: Sam, Adam, David
Rating: Mature (for some offensive language and adult themes)



physio 3
SF Norge A/S, 2010


It is discussed in the film that the trolls are primates. If this is the case, the smaller more common trolls that are encountered through most of the film will have metabolic rates similar to what has already been discussed in regards to The Ents and The Quiets (5,000-10,000 kcal/day). However, the largest troll seen in the film would have a metabolic rate more similar to Kong, and as discussed previously, would run into the same metabolic issues.


In the film, the trollhunter repeatedly tells the documentary crew that trolls eat everything. This includes rocks. In fact, one of the meals that the trollhunter uses to bait a trap is a mix of concrete and charcoal. The Trolls in the films are seen to have an incredibly varied diet ranging from goats to tires, but it is unlikely that they would be utilizing rocks as a nutrition source.

Rocks offer no nutritional value. Although we do need to consume very small amounts of minerals like iron and calcium to survive, generally consuming rocks is a useless and in many case harmful action for most life on Earth. The only exception are animals that consume rocks to act as gastroliths.

Some species of birds and other animals (like seals and whales) consume rocks, in order to use them as gastroliths. For many birds, this process involves swallow sharp pebbles and grit that are then held within a muscular part of the stomach called the gizzard. As birds are generally forced to consume most food whole and lack teeth to grind the food up, they use the stones and muscular contractions to break down seeds and other dense material. Eventually, the sharp jagged chunks of rock become smooth and are not suitable for grinding anymore. At this point, the birds vomit up the round rocks and consume new sharp ones.

Gastrointestinal- Final Thoughts

The trolls have an incredibly varied diet, but it is very unlikely that they would use rocks as a nutritional source. Instead, it is more likely that the trolls use rocks like birds, as gastroliths. In order to break down bone and other materials from animals that the trolls appear to eat nearly whole, they might have developed a secondary digestive system. The troll hunter might have frequently seen trolls consuming rocks in the wild for this purpose, and falsely inferred that they were using the rocks as a nutritional source. Based on the PTSD he is clearly suffering from, it is not surprising.


In the film, the first troll species encountered (The Tusseladd) is seen to possess three heads. We are told that the organism starts with only one head, and other heads develop as they age. The other heads don’t have eyes, but do appear in all other ways to resemble the central or primary head. They are able to swivel to follow prey, can open their mouths, and appear to possess other complicated structures like hair, skin, muscle, and presumably bone.  The troll hunter tells the film crew that the protuberances are intended to scare other members of the troll clans and impress females.

Although it is true that other male members of certain species on our planet can develop secondary sexual characteristics to fend off other males or attract females, it is very unlikely that secondary heads would be one of these features. Most secondary features are developed at only one time during their lives (with some rare exceptions like horns that continue to grow) and are basic in their design. Simple feathers, horns, or color changes are usually the height of these adaptations. Growing entire heads with bone, skin, hair, and muscles would be very energetically costly.  

Final Thoughts- Third Head

It is unlikely that any species would go to all of the trouble of growing extra heads, only for the purposes of scaring off others and attracting females. If they were to develop secondary characteristics we would expect them to be simple (like bumps on the skin with pigmentation changes to resemble faces) and to occur at one development period during their life. The development of extra heads would require changes in vasculature supply, muscular organization, skeletal structure, and neurological development. This would be incredibly complicated to do throughout the trolls life. It is more likely that the trolls are born with the extra heads and there is normal variation within the species in how heads they possess. The other option would be the development of simple protuberances that just resemble heads in the dark. One again, I am not sure how well the troll hunter truly understands troll biology.  


In the film, the trolls are observed to have lethal reactions to sunlight. We are told by the “veterinarian” that on exposure to UV Radiation the trolls experience a process related to their “incapacity to convert Vitamin D in light to Calcium.” This causes the younger trolls to explode because their stomachs expand and gasses are pushed into their intestines and veins.

The older trolls turn to stone instead because their veins are too constricted so the expansion occurs in their bones and the troll calcifies completely in a matter of seconds This entire process is stated to be extremely painful for the victim. In an interview with the director he stated that he came up with these ideas after discussions with his wife that is a veterinarian.

Unfortunately, the director appears to have misunderstood some of what his wife was explaining to him. Although your body needs vitamin D to absorb calcium (in the form of calciferol or vitamin D2), vitamin D is not calcium. Furthermore, there is no biological mechanism that would allow the improper processing of any vitamin to result in an explosion or conversion to stone. There are diseases in nature that can result in damage due to exposure to sunlight and a hardening of skin as a result of trauma. None of these have anything to do with vitamin D conversion.

In terms of sunlight diseases, there are two seen in humans. Xeroderma pigmentosum is a rare genetic disorder seen in humans. The body has a decreased ability to repair DNA damage caused by ultraviolet light. As a result severe sunburn develops after only a few minutes in the sun. Nervous system issues such as hearing loss, poor coordination and seizures are also often associated with sunlight exposure. Fewer than 40% of individuals with the disease will survive past the age of twenty. The second sunlight disease is Solar Urticaria. Exposure to any form of UV light causes an allergic reaction that induces hives in both covered and uncovered areas of skin.  The mechanism is thought to have something to do with histamine.

As for skin hardening diseases, Fibrodysplasia Ossificans is an extremely rare genetic connective tissue disease. The body’s repair mechanism in response to damage is faulty. As a result, trauma to fibrous tissue (muscle, tendons, etc) leads to the tissues becoming ossified (filled with calcium like a fossil) rather than scarred. Humans with the disease must avoid any form of damage and typically live very short lives.

Final Thoughts- Stone Skin

It is not impossible that the trolls would be afflicted with diseases similar to xeroderma pigmentosum/solar urticaria and fibrodysplasia ossificans. Although both of these disease are rare, they are both genetic, and the trolls in the film do seem to show some traits consistent with small populations and inbreeding. However the chances that they would have both diseases, have both disease within all members of the species, ad live for thousands of years, does not work.

Any trauma in Fibrodysplasia Ossificans leads to calcification. This would not just be limited to exposure to sunlight. Furthermore, the process would require days if not weeks to leads to complete calcification of the trolls skin. Lastly, there are multiple biological mechanisms of selection that would prevent this trait from being passed on. There is no advantage to turning to stone when exposed to sunlight.


In the film, we are repeatedly told that trolls are capable of smelling the blood of a christian man. This ability is on display when one of the film crew loses his cool in the cave and begins to pray. This action seem to result in the trolls almost instantaneously picking up his scent. The problem is, there is no biological mechanism for smelling religion.

It is not unrealistic to believe that the trolls have an incredible sense of smell. The trolls are equipped with large noses, they are constantly seen sniffing the air, and the hunters must cover themselves in “troll stench” to get anywhere near the monsters. However, the mechanism for detecting religion wouldn’t work because religion has no odor. Theological transformations produce no alterations to a bodies underlying chemical composition.

Final Thoughts- Smell

It is very reasonable to believe that trolls have an incredible sense of smell. However, there is almost no way for them to smell christian blood. Instead, it is likely that in the cave the cameraman’s stress, excessive sweating, and noisy praying were his undoing. It had nothing to do with his religion, just his ability to handle pressure.


The primary mechanism of the film used to explain why the trolls (who have been hidden for so long) are now more frequently seen is rabies. The big reveal at the end of the movie is that rabies has been spread by the enormous Jotnar across Norway. This is an interesting idea to explain abnormal behaviour and a clever plot device. The only problem is the science surrounding it is not done correctly

In the real world, rabies infection is a serious issue. Rabies is a virus that is transferred from animal to animal, usually through bite wounds. Infected saliva enters the tissues and the virus replicates within local nerves. The infection slowly ascends up infected nerves to the salivary ducts and the brain. Infected humans typically take between 1-3 months to show first symptoms (although rare cases as short as 4 days have been documented, varying based on the location and severity of the bite). Initial signs are non specific like a fever and headache, but they quickly progress to partial paralysis, insomnia, confusions, hallucinations, and eventually a coma. Death usually occurs 2-10 days after the first symptoms are seen. This is not the way the disease is shown in the film affecting the infected human protagonist.

Furthermore, rabies is a very difficult disease to diagnose. Several tests are necessary in humans to detect the virus in ante-mortem cases (before death). Analysis of saliva, serum, spinal fluid, and skin biopsies of hair follicles at the nape of the neck are all performed (no single test is reliable). Diagnosis in animals is typically made after death. Brain tissue is sampled from at least two different locations and requires extensive analysis for a definitive diagnosis. In the film, the veterinarian makes a diagnosis based on a blood sample, something that just can’t be done. She also noted that the rabies has caused anemia, not one of the side effects of the disease in any animal.  

Rabies- Final Thoughts

The idea that rabies could be responsible for the abnormal behaviours displayed in the film is a great idea. However the symptoms that are shown were not correct, the length of the disease progression was not correct, and the diagnosis was not correct.


Cleaver, J E, and D Bootsma. “Xeroderma Pigmentosum: Biochemical and Genetic Characteristics.” Annual Review of Genetics, vol. 9, no. 1, 1975, pp. 19–38., doi:10.1146/

Frederick S. Kaplan, Martine Le Merrer, David L. Glaser, Robert J. Pignolo, Robert E. et al. Fibrodysplasia ossificans progressiva, Best Practice & Research Clinical Rheumatology,
Volume 22, Issue 1, 2008, Pages 191-205, ISSN 1521-6942,

Nina C. Botto, Erin M. Warshaw, Solar urticaria, Journal of the American Academy of Dermatology, Volume 59, Issue 6, 2008, Pages 909-920, ISSN 0190-9622,

Charles E Rupprecht, Cathleen A Hanlon, Thiravat Hemachudha, Rabies re-examined, The Lancet Infectious Diseases, Volume 2, Issue 6, 2002, Pages 327-343, ISSN 1473-3099,


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