They are testicles on male cats.
No . They will roll the scrotum into this shape that makes the cat look like he still has testes, but there are no testes in it.
No. There is a cartoon called "Cat-Dog". But, there is no cat-cat or cat-dog in reality.
Well, my cat has been chased in by our other cat. so it is possible for that to happen to yours.
racoon
I'm guessing a raccoon.