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." Tom, 15, also said he picked up tips from Jason Isaacs, who made his first appearance in Chamber of Secrets as Draco's dad, Lucius Malfoy.
"He's incredible - the most amazing actor I have ever met," Tom said. "He can switch from being nice to being evil in a second
Both Tom and Matthew, who plays Neville, agree working on the second Harry Potter film was easier than the first.
"It's all like one big family," said Tom. "Everyone plays their own crucial part towards the film."
Matthew agreed. "The second film was a lot calmer than the first," he said. "You know everyone and you're not afraid of mucking up in front of the bigger actors, like Kenneth Branagh. He was brilliant."
'Stuffed cotton wool in my cheeks'
Matthew, 13, told CBBC Newsround Online a few Potter filming secrets. Because he lost weight towards the end of the shoot, the crew had to make sure he didn't look really different.
"They stuffed cotton wool in my cheeks to make me look fatter in the scene in the greenhouse with the Mandrakes, which was one of my last scenes," he admitted. "It was quite funny."
He also had to grow his hair to play Neville, and he cuts it short as soon as filming finishes, because he doesn't like it long.
'JK is very secretive'
Matthew revealed he had a lot of trouble filming the scene in The Philosopher's Stone when Hermione performed the Petrificus Totalus spell on him. He had to fall to the ground totally rigid.
"I kept doing it and doing it - I even practised at home with my brother - but eventually they had to get a stunt man in because my legs kept flying up at the ends," he admitted.
Matthew also insisted JK Rowling was just as secretive with the cast as she is with the public about the future of Harry Potter.
"I have no idea who dies in book five," he said. "JK Rowling is very secretive. She keeps dropping a few hints but she doesn't tell. I hope it's not me!"