Father, mother and son decide to go to the zoo one day. So they set off and are seeing lots of animals. Eventually they end up opposite the elephant house. The boy looks at the elephant, sees its willy, points to it and says, "Mummy, what is that long thing?" His mother replies, "That, son, is the elephant's trunk." "No, at the other end."
"That, son is the tail." "No, mummy, the thing under the elephant." A short embarrassed silence after which she replies, "That's nothing." The mother goes to buy some ice-cream and the boy, not being satisfied with her answer, asks his father the same question.
"Daddy, what is that long thing?" "That's the trunk, son," replies the father.