Not super graphic but **SPOILERS** the rats bite what I'm assuming is a neck artery. It doesn't show it in great detail but they do bite someone's neck and it bleeds a lot
Willard's mother doesn't physically abuse him but is very controlling and smothering and is constantly wanting to know what he's doing and following him/intruding on his privacy.
A cat is chased by rats and bitten by one, then falls into a swarm of rats and disappears under it. The scene stops there and doesn't show the cat's death in any graphic detail.