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The elephant may be distinguished from other animals by its knee joints, which are much lower down than in most hoofed creatures. It is thus able to bend its hind legs in the fashion of a kneeling man. Ivan the Terrible put an elephant to death because it bowed down before him. The African elephant sleeps in a standing position. The elephant needs only two hours sleep a day. The elephant cannot jump, but is the only animal apart from man that has been taught to stand on its head. It is forbidden to lead an elephant through the approach tunnels of London�s Heathrow Airport. In Milwaukee, pet elephants must be kept on a lead when taken for a walk on public streets.