The late Canadian actor was known for his absurdist comedy and one of his best-known gags was the fart machine. Nielsen would often use it in interviews and cause the interviewer(s) to act quickly. The machine itself was just a short rubber cylinder with a hole in it which you squeezed to make a fart noise. I have one and it’s really difficult to get a plausible fart sound but Leslie mastered it.
Stream an early appearance of the contraption with David Letterman below and a TV-AM appearance below that.