
Patrick B. says that you can trick someone into mentioning farts without them realizing it by getting them to read the following out loud, preferably in front of an audience: HOOF HEARTED ICE MELTED.
M. Rodrigues submitted this one: Get your friends to say this fast: One smart man, he felt smart; two smart men, they felt smart; three smart men, they all felt smart!
Scott offers this version of the one above: One smart fellow, he felt smart; two smart fellows, they both felt smart.