By chance, a man called John Smith witnessed a mugging. About an hour later, the cops arrived, and the officer in charge asked the witness his name.
"John Smith," John told him.
"Cut the funny business," the cop barked sharply. "What's your real name?"
"All right," said John, "put me down as Wolfgang Amadeus Mozart."
"That's more like it," said the man in blue. "You can't fool ME with that Smith stuff."