A black cat.

The story goes something like this...

P.T. Barnum, the owner of the Barnum and Bailey circus and a well known trickster, offered a prize of $10,000 to anyone who could successfully dupe him. One day he received a letter from a man in Maine, who claimed to own a cherry-colored cat, and wanted to know if Barnum would be interested in including it in his circus. Barnum was always looking for new curiosities, and agreed that, if it were truly a cherry-colored cat, he would put it in his show.

Not long after, Barnum received a crate labeled 'live animal' -- but when he opened it, he found a black cat. On further inspection he also found a note explaining, "Maine cherries are black."

The man got his $10,000.

Regardless of whether or not there is any truth to this, Barnum did use the (black) cherry-colored cat trick as a side-show exhibit. The public knew to expect this sort of thing from Barnum, and generally considered being fooled to be part of the fun.

This way to the egress