Brad Pulls 'Wham!' Pranks on Jonah

There's no crying in baseball! Moneyball star Jonah Hill tells ET that working with Brad Pitt on their Oakland A's behind-the-scenes drama was intimidating at first, but the A-lister quickly made the experience "cool" and enjoyable -- and pulled some pretty entertaining pranks on him to lighten the mood.

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"He's a maestro of pranking," says Jonah with an air of reverence. "He has a fortress of pranking genius around him. … He knows your moves while you're thinking of it. Prank chess, he's playing all the time."

Jonah reports that Brad decided on a Wham! theme for a few of his pranks, which gathered steam and then got pretty relentless, culminating in wrapping Jonah's on-set golf cart in pink and rigging it to blast Wake Me Up Before You Go-Go whenever he would turn on the "Wham! Mobile."

"He's really funny, he's really fun, and I think our relationship in the movie's kind of a big brother-little brother relationship, and I think we had that kind of fun energy with each other off set," says Jonah.

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In addition to stretching as an actor, the star of such films as Superbad and Get Me to the Greek is sporting a slimmer, trimmer frame, and Jonah chalks it up to priorities.

"Once something becomes a priority, at least for me, it just is a priority," he explains. "I went to a nutritionist and I just started running and doing push-ups and sit-ups and stuff like that. It's definitely a tough thing to do. Once you make that decision, you've got to stick to it."