You can smell it. If it smells rancid, you may want to replace it.
seriously...I have no clue
yes
A mushroom is safe to eat if you find it in one of two places- at a supermarket or a local growers' market. Unless you happen to be some trained expert, don't eat mushrooms you find out on the wild....
They can.
Cats can eat rice if you let them, but it holds absolutely no nutrition at all.