Kangaroo
A kangaroo keeps escaping his enclosure at the zoo. In an effort to keep him inside at night, the zookeepers construct a 10-foot fence around his habitat.
The next morning, they find the kangaroo wandering around the zoo.
The zookeepers construct a 20-foot fence to keep the kangaroo from escaping, but the next day he is loose once again.
The zookeepers begin construction on a 50-foot fence they’re sure will keep the kangaroo in his enclosure. Watching the men work, a camel in the neighboring enclosure sticks his head over to the kangaroo’s side and asks, “How high do you think they’ll make it this time?”
The kangaroo answers, “Not sure, but it still won’t matter, unless they remember to lock the door this time.”