A man and his son are walking through a highly built-up Manhattan when they come across an empty space and the father stops to reflect for a while. "Imagine, son," the father says, "exactly 31 years ago, the great twin towers stood proudly in this area."

Intrigued by the comment the son then asks, "What were the twin towers, dad?"
To which the father replies, "They were two of the largest buildings in the world, and they housed many thousands of offices.... but in 2001 they were destroyed by Arabs."

The son pauses for a while and then asks, "What were Arabs, dad?"