Also potatoes when they do rot smell like absolute death

And if you see one like this don't eat it, it's probably relatively green and could make you seriously ill or worse to eat it, not because it's rotting though, but because of toxins!

Basically if it's green, skip it, if it's pale green only in the skin you might be ok if you peel it, but if the actual flesh is green toss it. Don't risk it.