Helena Bonham Carter recently wrapped her role as cannibalistic pie-maker Mrs. Lovett in the movie version of Sweeney Todd (directed by her fiancé, Tim Burton and starring Johnny Depp), which opens in December. But this summer, she lands on multiplex screens as a villainess of a different flavor: Mad witch Bellatrix Lestrange, the Voldemort-loving scourge of Harry Potter and the Order of the Phoenix. The devilishly frank actress took time out to dish to EW about wand safety; her soft-spoken but strong-willed Phoenix director, David Yates; and the perils of keeping your screen time intact when you sign on for a small supporting role in a huge ensemble movie.

ENTERTAINMENT WEEKLY: So you wore fake teeth to play Bellatrix. You wear them in lots of movies, don't you?
HELENA BONHAM CARTER: For Planet of the Apes I had amazing teeth. And I had them for Mrs. Bucket [in Charlie and the Chocolate Factory]. Just 'cause I had to do something in the background. I looked at Noah [Taylor, who played Mr. Bucket] and thought, If I'm supposed to be your missus, we need to be Mr. and Mrs. Crap-teeth.

But you sound so clear when you speak as Bellatrix.
At first, it's like, Oh, what is this foreign thing in your mouth? You've got to keep them in so you get used to them. But then you can forget they're in. If you then eat something, that's just disaster, 'cause they break. That's very expensive.

How would you describe Bellatrix?
She's obviously as bonkers as they come. There's a bit of a child-like madness there. I did regress a bit as her. It sort of happened naturally. It's easy for me to go back to being a kid. You know how kids can be like savages before they get civilized? There's that sadist quality. Y'know, like boys who like to pick apart an insect for the sake of it.

And that describes Bellatrix for you?
Oh yes. She's a sadist. She's very sick. She's got problems. I think she's been in prison a bit too long. But I suspect even before prison she had problems. She's a racist, obsessed with blood purity. Like Adolf. And she's in love with Voldemort, really.

In a lot of Phoenix promos, Warner has been playing up that image of Bellatrix threatening Neville Longbottom (played by Matthew Lewis) with her wand.
I did something terrible. By mistake, I poked him in his ear. I thought I could brandish the wand like a sort of Q-tip, and clean out his ear. Sort of torture it. But unfortunately he moved toward the wand as I was prodding it. And it actually perforated his eardrum. Isn't that horrific? I damaged him! He's such a nice young man, he didn't admit to me that he actually had some internal bleeding about three days later.

So you didn't even know you'd injured him at the time?
No. And it wasn't permanent. But there was pain, and blood. Well, torture happens. Sorry! Oops! I think I took my sadism a bit too literally.

Wow — that's an interesting bit of improv.
Stupid, though! Dangerous! I did feel awful when they told me.

Did you get a chance to apologize to Matthew later, once you found out what had happened?
Oh yeah. But he was deaf, so he couldn't hear me. [Laughs wildly]

You're kidding, of course.
And then ever after I was always shouting, ''ARE YOU ALL RIGHT, LUV?''

NEXT PAGE: ''My assistant said, 'You look like a porn star!' That was not the image I was going for.''

Speaking of shouting, it's something I bet David Yates never, ever does. He seems incredibly soft-spoken.
Oh, no. That's all cover. [Laughs] He knows what he wants. Actors often think they can massage the director into doing them their way, and often directors really are massaging you into giving them what they want.

How did you come up with Bellatrix's slinky look, especially the big bustier and the cleavage?
I have chicken fillets. I'm not blessed. And so I thought, Well this is my chance to have the boobs I've always wanted. But then my friend, my assistant, said, ''You look like a porn star!'' That was not the image I was going for. [The film's costume designer], Jany [Temime], was originally just going to put me in a sack. I said, ''There's no way. I want to have a sexy silhouette.'' Because I'm short, and I could easily look terrible. So I had the idea of the corset. She looks like a warrior. I mean, Bellatrix does mean warrior. And she's also a bit of a fatale. She's the right hand of Voldemort, and the only woman death eater.

Why does Bellatrix so enjoy attacking her cousin Sirius Black?
He deserves it. [Laughs raucously] He betrayed the whole family, went all goody-goody. He had this coming for a long time.

There were bits of footage of you in the coming attractions and in TV previews that showed you dueling with Gary Oldman's Sirius, and also taunting Harry. But those seem to be missing in the final cut of the movie. What happened?
I had a duel with Sirius, during which he makes a strategic mistake. I learned for three weeks how to wand-fight. And I was really good with all my spells! It was really complicated stuff. And then they cut the fight! They just cut it. I can't believe they cut the fight. All that wand training for nothing. And a wand blister. I told the [producers and director], ''You've got to put that in the DVD extras.'' I did learn to do my spells. And it's a good fight, too. I stuck my tongue out at the end.

Actually, I asked director David Yates about that. He says the DVD will have about six cut scenes. But your fight bits won't be one of them, because they were woven into a longer scene that is in the final movie. I think you're out of luck unless they reissue the whole movie expanded down the line.
Did they leave in the thing with me holding my nose when I apparated?

Don't recall seeing that.
Ah. You give 'em everything, and they keep the bland one.... Well, if you want a big part, don't let yourself be in the shooting script for only the last three pages. [Laughs] I've been employed [already] for the last [movie]. So I guess I figure in the seventh book. J.K. Rowling said Bellatrix's role was going to be significant in the last one, when I showed some reluctance in playing a tiny bit part. [Cackles] Up front, they said, ''You're very significant in the last one.'' But significant could mean a lot of things. That could just mean a significant plot point. Doesn't necessarily equal big part.

We'll be rooting for you.