A Creepy Birthday Party

A little girl was invited to her friend’s birthday party. After blowing out the candles and eating the cake, the children went out to play in the garden. The little girl’s mother stayed in the kitchen talking to the other adults. They could hear the kids screaming and shouting as they played outside. Soon the little girl came running in the house. "There she is", said her mother. "It’s her birthday next month. Tell everyone how old you are going to be" .

The little girl smiled and held up 4 fingers. All of the adults stared in horror.

Why was everyone staring at horror?