Michelle Williams Jiggles Just Like Marilyn Monroe

She added a few pounds, had the blonde wig, and spent hours in makeup each day to play Marilyn Monroe in the upcoming film My Week with Marilyn. But Michelle Williams had to learn to move like the Hollywood legend, too.

“I wasn’t watching what I ate, let’s put it that way,” Williams, 31, told PEOPLE Sunday, at the film’s New York premiere, about her physical transformation, which also included some helpful wardrobe tricks that helped her jiggle a bit more.