Platonic forms are imaginary, perfect representatives of a concept. There are lots of different types of birds. However, if we had one bird to represent the "bird-ness" of all of them, this would be the platonic form of a bird. We could also imagine a platonic form of a chair, serving as a perfect example of chairs, capturing all of their "chair-ness".

If there is a set of things, such as birds, then there is likewise a distinctive attribute uniting all the parts of this set--like their bird-ness--and the platonic form of that thing is the imaginary entity that possesses that distinctive attribute (the bird-ness) and nothing extraneous to it. For example, the platonic bird will not be red or blue, since these attributes are contingent and not definitive of bird-ness.

These things don't really exist. But they are similar to the idea of a "prototype" from cognitive science. The idea is that our brain builds up concepts through examples, for example building the concept of "bird" by seeing lots of birds; maybe all of this information is stored in a "prototype" for bird in our brains.

If buffalos have got you thinking, I'm gonna blow your mind by telling you about elephants and brontosauri. Or even gorillas--these bulky beasts get super swole by eating plants.

You don't need meat to get big. Especially when you have a digestive system that is capable of getting nutrition from non-meat sources. Lots of animals have evolved different digestive systems than us. They get more out of the plants that they eat than we do.

(Heck, even humans don't need meat to get big. We just need protein--and this can come from many non-meat sources.)

Professional football players and boxers have a 100% chance of suffering traumatic brain injury during their careers (literally--a study of the brains of deceased football players showed that all of them had CTE). They still do it. Money, fame, glory, the belief in young people in their immortality, are probably all contributing factors.

As in modern sports, medieval athletes took steps to protect themselves. The goal wasn't to kill each other. They wore special armor and used blunted weapons.

Of course, sometimes people died, but people die in modern sports, too. To say nothing of the severe and debilitating brain damage they suffer from repeated concussive injuries.

It definitely is a thing. Bones vary in density quite a lot! However, as it is commonly applied as a way to describe overweight people, it is most often inaccurate--bone density scans show that overweight and obese people tend to have thinner bones.