Bava Kamma 20: Squatter's Rights

What if your animal eats food from the pack on the back of another animal? Or comparable damage. Who's responsible? Is this standard behavior or not? Is it like walking and damaging or standing and damaging or jumping and damaging, which is another category, or might be. Also, what about the case of a squatter - and what happens then? Does the owner know? Is rent involved? Is squatting causing any harm or monetary loss?