Last summer's blockbuster hit "X-Men: Days of Future Past" wasn't exactly a comedy, but you'd never know it from this behind-the-scenes video of Jennifer Lawrence uncontrollably laughing.

What did Mystique find so funny, you ask? Well obviously it was having to tell James McAvoy's Charles Xavier that he's "living in a fantasy land."

"I'm sorry, I am going to be able to say it," Lawrence says as she tries her best to stifle a serious case of the giggles. "It is a good line. In the movie it will work."

Eventually it gets so bad that McAvoy has to promise not to look at her, but even the Scottish actor's averted gaze can't stop Lawrence from cracking up:

"X-Men: Days of Future Past" will be available to own on October 14.