What happens when Tina Fey and Jimmy Fallon swap mouths? Hilarity ensues!

The "Muppets Most Wanted" actress stopped by "The Tonight Show" on Monday night, where they traded mouths in the popular skit, "Lip Flip."

"I know you're interviewing me here, and you're doing a pretty good job, but I would also like to interview me," the former "30 Rock" star said.

"I think I know what you're talking about and I have a way to make that happen. It's time for a lip flip," Fallon added.

Fallon's lips were then superimposed over Fey's, and vice versa.

Once they got used to their new lips, the funny duo sang a duet of "Endless Love," Check out their special rendition of the classic song above around 2:40! 

What do you think of their lip flip? Sound off below.

Want more Fallon? Click here to see the late night host sing "Let It Go" with Idina Menzel and The Roots -- with classroom instruments!

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