stool pigeon → white elephant
a stool pigeon (spy for the police): Keep your mouth shut when you talk, he might be a stool pigeon.
quiet as a mouse (very quiet, making absolutely no noise): She was as quiet as a mouse, hiding in there.
as sick as a dog (very sick): I’m going to see a doctor, I as sick as a dog.
as the crow flies (by a direct route): That town is forty miles from here, as the crow flies.
weak as a kitten (very weak, without much strength): Two month of illness left him as weak as a kitten.
wild as a tiger (very wild): We were trying to look after your baby, but she was as wild as a tiger.
at a snail’s pace (very slowly): There was also heavy traffic, and we were driving at a snail’s pace.
a white elephant (something expensive, but is not useful): Building a swimming pool is a white elephant and a waste of money.