A group of elementary school students were on a field trip to the local police station. Several of the children were fascinated by the wanted posters on the wall.

Little Johnny raised his hand and asked the police officer giving them the tour who the people on the wall were.

"Those are pictures of criminals we are looking for," answered the policeman. "We call those wanted posters."

Little Johnny looked puzzled. He raised his hand back up into the air. "Well," he wondered, "why didn't you just keep them when you took their pictures?"