Renee Zellweger, Rough and Tumble

Doing physical comedy isn't as easy as it looks, according to Me, Myself & Irene star Renee Zellweger.

The actress tells TV Guide Online she had no idea what she was in for when she agreed to spend two days shooting a scene that had her floating down a choppy Vermont river. "You don't really notice the scrapes and bumps and bruises until you're getting dressed in your costume and you go, 'Oh, my gosh, what happened yesterday?' " she says.

Zellweger confesses she did get a kick out of giving co-star Jim Carrey the boot ? literally. In one scene, she gives the funnyman a kick that sends him flying down a hill.

"It was hysterical, actually, because he kept insisting that he be the one to fall over the back of the railing and roll down the hill and nearly hit the tree each time," she says. "Everyone else kept insisting, 'No, no, no, it's OK, just tell them what you want and they'll do it,' and Jim kept insisting, 'No, no, no, I have an idea and it should be me, I want to do it.' "

Sure enough, wacky Carrey did multiple takes until he got it right. Then, in a bizarre twist of fate, the fearless funnyman tripped and sprained his ankle during the lunch break.

"He throws himself off trains and he does these flips onto the concrete and crashes through the glass, and smashes plates over his face, almost falls into the tree, four or five times, and then it's the gravel road that gets him," she says. "Very funny."