A kangaroo kept getting out of his enclosure at the zoo. Knowing that he could hop high, the zoo officials put up a ten-metre fence. But the next morning he got out again and was found roaming around the zoo. A twenty-metre fence was put up. But again he got out.

When the fence was forty metres high, a camel in the next enclosure asked the kangaroo: “How high do you think they’ll go?”

The kangaroo said: “About a thousand metres unless somebody starts locking the gate at night!”