It's easy to trust your childhood friends, or loyal minions with your secrets but even they have a limit to what they'll keep secret. Perhaps a group of drunken teens ran over a little kid, and decides to close ranks, make a pact, cover everything up and keep the crime to themselves. But one or more group members are uncomfortable with the secret and appears to be cracking under the pressure, and could possibly rat out the other party members that were involved. Whether or not they actually squeal, stay silent, or get killed by their supposed friends varies from movie to movie. Usually when this happens everyone becomes paranoid of one another when it comes to being a potential snitch. This trope is very common in horror/thriller/crime dramas/murder situations.