The Potter kids have grown into the very model of actorly professionalism since they first stepped onto the stage more than 10 years ago for Harry Potter and the Sorcerer's Stone. But as this promotional clip for Deathly Hallows shows, they're not entirely incapable of childish fits of hilarity.
If we didn't know better—and, naturally, we don't know better—it looks as if young Miss Watson was taken with her co-star, Rhys Ifans. Otherwise, how to explain her inability to keep it together during the time she was shooting with him on Deathly Hallows Part 1? In her own words: "I never really have problems corpsing, but I really struggled for those two or three days."
Corpsing, so you know, is a British term used to describe breaking character and scuttling a scene with laughter. Ah, the Brits ... always keeping things cheery.