tip the gaff

Verb

 * 1) To give away how a magic trick is accomplished.
 * 2) To reveal a disguise or something hidden.
 * 3) * 1914: The Smart Set: A Magazine of Cleverness, Volume 42, "The Parasite" by George Bronson-Howard
 * Lady! She couldn't disguise herself as a lady with that Slavonic map of hers tipping the gaff, and those heavy hoofs of hers.
 * Lady! She couldn't disguise herself as a lady with that Slavonic map of hers tipping the gaff, and those heavy hoofs of hers.