Sir Michael Gambon and Alan Rickman once pranked Daniel Radcliffe with a “fart machine” on the set of Harry Potter and the Prisoner of Azkaban.
During a scene in which Hogwarts students are sleeping in the great hall, Albus Dumbledore and Severus Snape - portrayed by Sir Michael and Rickman - quietly walk through discussing “dreams”.
As one of the takes was being recorded, Sir Michael pranked Radcliffe by pressing a button to set off a fart machine placed in the teenage actor’s sleeping bag.
Behind-the-scenes footage from the 2004 film shows the hall erupting with laughter as the prank unfolds.