If the Summit Entertainment marketing machine has done its job, you've probably seen the eye-catching movie posters for the studio's latest release "50/50." The goofy one-sheet depicts a memorable scene from the film in which Joseph Gordon-Levitt's cancer-stricken Adam shaves his head, while a dubious Adam (played by Seth Rogen) looks on.

It's one of the movie's many lighthearted moments, adding levity to what could otherwise be a downer drama. But according to the film's stars, the take wasn't as carefree as it may have looked.

"My heart was beating hard, because we only had one take because you can't shave your head twice. It doesn't work," Gordon-Levitt said at the "50/50" premiere earlier this week in New York. "Normally, you can always do it over again when you're making movies. You get a take two. But we only got take one, and it worked."

Apparently, Gordon-Levitt had another reason to be nervous about the scene — it wasn't scripted. According to producer and co-star Rogen, the two just played it by ear.

"We only had one shot at it," Rogen recalled. "It was the first day of filming, and we improvised the whole thing, which is not wise when it's something you have one take for, but it turned out funny. It went exactly how you see it in the movie, which was pretty good, I think."

You can judge Gordon-Levitt's razor skills for yourself: "50/50," co-starring Anna Kendrick, Bryce Dallas Howard and Anjelica Huston, opened Friday (September 30).

Check out everything we've got on "50/50."

For breaking news, celebrity columns, humor and more — updated around the clock — visit MTVMoviesBlog.com.