06/15/2001 AT 11:00 AM EDT
As Roberts feigned sleepy innocence, Weintraub searched her room. Then, hearing a door slam, he swung around to see Clooney and Damon hightailing it down the hall. On another night, Clooney rigged a bucket of water over Roberts's door -- only to soak a hapless bellman who entered first. "The pranks here," sighs Weintraub, "are akin to Animal House."
As he approaches his 40th birthday on May 6, there's no question that George Clooney still likes to have his fun. "He's not immature, but he hasn't quite grown up yet," says Walter Bernstein, who wrote the screenplay for Fail Safe, the classic Cold War thriller Clooney reproduced as a live TV drama last year. "There's still something unformed about him." Julianna Margulies, his friend and former ER costar, has noticed too. "George," she says, "is a grown-up with a kid's heart."