In the modern rom-com ''What If,'' Daniel Radcliffe, 24, trades his wizard robes for jeans — and nudity; here, he explains how he prepared to become a romantic leading man

By Nicole Sperling
May 23, 2014 at 04:00 AM EDT

Study Hard
What If, about a med-school dropout (Radcliffe) who falls for an already attached art director (Ruby Sparks‘ Zoe Kazan), is more than Radcliffe’s first rom-com. After Harry Potter and period films such as The Woman in Black, he notes, ”it’s pretty much my first foray into the 21st century.” To get ready, he boned up on his genre faves: When Harry Met Sally…, It Happened One Night, and Arthur with Dudley Moore. ”It’s really, really funny. In so many romantic comedies the humor is kind of lame.”

Dare To Annoy
He shares a quirk with his character. ”It’s like I have a version of grammatical Tourette’s,” he says. ”I can’t hear someone make a mistake without wanting to correct them.”

Get Naked
The actor has dropped trou for stage productions of Equus as well as last year’s movie Kill Your Darlings — including a dream-sequence skinny-dip in NYC’s Hudson River later cut from the film. So he wasn’t put off by What If‘s naked swim. The bigger challenge: braving Toronto’s chilly beaches. ”We were really dreading it,” he says. ”It had been cold a few nights before, but it got beautifully warm. Lake Ontario was fantastic.”