Stool pigeon and Snake in the grass

Stool pigeon noun - A person who provides information about another's wrongdoing.

Snake in the grass and stool pigeon are semantically related. In some cases you can use "Snake in the grass" instead a noun phrase "Stool pigeon".

Snake in the grass noun - A deceitful or treacherous person.

Stool pigeon and snake in the grass are semantically related. Sometimes you can use "Stool pigeon" instead a noun phrase "Snake in the grass".