Attack on Titan tells the story of humanity living in fear of the Titans — a race of mindless, human-eating giants who hunt and eat humans for no clear reason. The manga, which was created by Hajime Isayama, has been a huge commercial and critical success, inspiring an anime television series adaptation, a live-action film, and video game.

The series is full of compelling mysteries that keep fans guessing: where did these Titans come from? Why do they hunt down humans? How did the Titan shifters come about? With 22 volumes of the manga and two seasons of the anime released, we have learned a lot about the history of the world and the Titans. Yet, it seems that each answer just adds ten more questions.

Fans have taken it upon themselves to create theories that fill in the remaining gaps in knowledge. Some of their ideas are wacky and out there, but many could easily be true.

Here are the 15 Craziest Attack On Titan Fan Theories That Change Everything.

Warning: spoilers ahead if you are not caught up on the manga.

15. A Titan’s Body Is Made Of Yeast

attack on titan Attack On Titan: 15 Craziest Fan Theories That Change Everything

This theory has made the rounds on both Facebook and Tumblr due to a section on yeast that is included in the anime and manga’s extra public information sections.

A unique type of yeast is produced behind Wall Sina that is used to preserve food by slowing down the decomposition process. The preservation capabilities of yeast could be what allows Titans to preserve the age of their pilot if their bodies are comprised of it.

Furthermore, yeast produces a great amount of gas and heat — this would explain why the Titans release gas and extreme heat when they are killed. Yeast also expands the volume of an object when it expands, not its mass. Hangi once kicked a severed Titan’s head and was surprised at how light it was.

Finally, UV rays increase yeast production; this could be the reason Titans are more productive during the day.

14. Titans Eat Humans Because They Want To Be Human

Attack on Titan eating Attack On Titan: 15 Craziest Fan Theories That Change Everything

One of the biggest mysteries of the series is why the Titans feel compelled to eat humans in the first place. It is established that they do not need humans as a food source, since they end up gagging up the remains later.

They also do not appear to go after animals. They could just be hardwired to destroy humanity. However, even if that were the case, that does not explain why they consume human bodies instead of simply destroying them.

One plausible explanation comes from the revelation that, if a mindless titan eats a titan shifter, they will become human. Redditors have theorized that perhaps Titans know this subconsciously and this is what drives them to eat every human they see — in the hopes that one of them will end up being a shifter.