See 'Sisters' Stars Tina Fey & Amy Poehler Switch It Up For The New Movie — EXCLUSIVE CLIP

Everybody knows how well Tina Fey and Amy Poehler go together. They're like peanut butter and jelly, or cookies and cream, or Fireball shots and a hangover. The comedy veterans team up once again in the new feature film Sisters , in theaters Dec. 18, and fans couldn't be more excited. The movie revolves around two women who, despite being siblings, are as different as could be. Maura is an uptight divorcee; Kate, on the other hand, is a foul-mouthed party girl. But upon learning that their parents are planning to sell the beloved house where they grew up, Maura and Kate decide to throw one last raging house party before closing the door on that chapter of their lives.

If you saw the Fey-Poehler collaboration Baby Mama in 2008 (or even just the infamous "Sarah Palin and Hillary Clinton" sketches on SNL), you're probably not surprised that the two hilarious actors are playing characters with complementary— if not conflicting— personalities. But what might surprise you in Sisters is who's playing which character. In a surprising departure from their previous work, the movie finds Poehler as buttoned-up Maura and Tina as wild Kate. The trailer even highlights this difference, labeling Poehler as the "perfect" sister and Fey as the "other" sister.

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It's awesome to see the comedians showing off their versatility with this role reversal, especially because their famous personas are so well-known that it's easy to forget that they both have extensive experience in creating different characters. In addition to their tenure as SNL cast members, Fey and Poehler worked together starting in the early '90s in the prestigious Chicago improv group Second City. In an exclusive behind-the-scenes feature from HBO First Look (the full thing debuts Thursday at 10:45 pm on HBO/HBO NOW), Sisters costar Rachel Dratch recalls that back in the days of Second City, Fey used to play "dirtbaggy" characters often. So despite the actress' typical nerdy and refined parts, the role of Kate isn't totally new territory.

However, some other people involved in the production were surprised at the casting choices, and kept getting confused about who was playing which sister. Another layer of confusion is added by the fact that in the film, Fey and Poehler's characters decide to switch roles so that Maura can embrace her crazy side at the party and Kate can be the responsible one there. So basically you're watching Tina Fey and Amy Poehler pretending to be Amy Poehler and Tina Fey's characters pretending to be Tina Fey and Amy Poehler's characters' characters. Got it? No? Well, check out the situation as described by the stars themselves in this exclusive clip.

Even if you're thrown off by the role reversal, you can't deny that Sisters looks hilarious. Don't miss the chance to rage with Tina and Amy when they bring the party to theaters so soon.

Image: Universal Pictures; Giphy