Devan Shell hates rabbits after reading "The Tortoise and the Hare", so he gathers a huge army. That's why they fight rabbits.

Eating carrots saves your life because it's much more appropiate for rabbits then med packs. No, I'm not sure how every game character has the ability to instantly heal themselves using a standard edition med pack, then not be able to use it afterwards.

Devan wears glasses for the same reason anyone else does.