Acting in the Harry Potter films can be a bit of a challenge.
Tom Felton and Matthew Lewis, who play Draco Malfoy and Neville Longbottom, chatted to CBBC Newsround Online's Clare Youell.
Getting into character can be hard for any young actor, but even more so when you're playing Draco Malfoy - the most horrible kid at Hogwarts.
But Tom Felton has finally admitted why he makes such a good baddie.
"I used to think about things to get me angry," he said.
"I have three older brothers so I did a lot of thinking back to when I was younger. Also, I just think of Draco and he gets me in the right mood. He just keeps getting worse and worse."