Late one night, a babysitter was by herself downstairs after putting the children to bed. The phone rang. Thinking it might be the children's parents, she answered it.
Instead of identifying himself, the caller merely breathed heavily into the phone for a few moments. She hung up, but the phone rang again. The babysitter answered it, only to hear the same breathing, followed by laughter.
The babysitter was alone in the house with the children and frightened, so she called the operator and asked that the call be traced.
When it rang a third time, she heard the same breathing and laughter before the caller hung up. The operator called back almost immediately, frightening the babysitter by telling her the call was coming from inside the house.
The babysitter ran outside while the operator called the police. When they arrived, they discovered a man had murdered the children and was waiting to murder the babysitter if she came upstairs.
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There is a movie called Don't answer the phone