Teratomas are horrifying, albeit fascinating, types of tumors that can spontaneously grow hair, muscle tissue, bone, and even fully formed teeth inside your body.

A closer look

Teratomas are horrifying, albeit fascinating, types of tumors that can spontaneously grow hair, muscle tissue, bone, and even fully formed teeth inside your body. The name translates from Greek to mean "monster tumor," which is incredibly accurate considering these cysts originate from rogue germ cells that get hopelessly confused about their life purpose. Instead of developing into normal reproductive tissue, they panic and start aggressively building random body parts in completely inappropriate places like your ovaries or tailbone. It is essentially your own genetics attempting a terrible DIY biology project without reading the instruction manual first. Having a random clump of cells decide to grow a fully functioning set of molars near your appendix is the absolute peak of biological betrayal, proving once and for all that your body secretly hates you!