Pranks were common on the Harry Potter set, and Radcliffe was both the victim and perpetrator of several behind-the-scenes shenanigans. But there was one prank Radcliffe felt may have trumped all.

Some of the older actors in the Harry Potter series could be just as much pranksters as their younger co-stars. The Dumbledore actor himself had a knack for making Daniel Radcliffe laugh. Sometimes, ...