FOX released some advance clips of tomorrow's 'Props' episode -- and in the behind-the-scenes videos (where 'Glee' cast members assume each others' identities), it's obvious the actors had a blast playing with their new personas. 

The plot of 'Props' is that Tina, distracted by her cell phone, falls into a fountain and hits her head. (Don't walk and text, kids!) When she wakes up, she has become Rachel, and all of her classmates have switched roles as well. Finn and Kurt trade places, meaning that the show's central couple of Finn and Rachel are played by Chris Colfer and Jenna Ushkowitz. "Being love interests with Chris Colfer playing Finn is the sentence I never thought I'd say," Ushkowitz observes.

Cory Monteith insists on doing Colfer's hair, to ensure that Finn looks as authentic as possible. "This is a time-honored 'Glee' tradition," Monteith claims. "It's very specific, so I wanted to make sure that Finn was properly represented."

Sue (Jane Lynch), who swaps roles with Will (Matthew Morrison), describes how she gets into the role, commenting, "I'm saying to myself as we're shooting, 'I'm handsome and nice.'" Meanwhile, Lea Michele says she's happy to play Tina because, "I love being able to slouch and give dirty looks."

While some of the character switches are obvious, others are more off the wall, like the pairing of Artie and Santana. Artie dons a cheerleader outfit and fake ponytail, while Santana wears a button-down shirt and sweater vest. "It's hard to do the scene, because the whole time, we're all looking at each other, looking at everyone's impressions of ourselves," actor Kevin McHale says.

'Props' airs at 8PM ET on Tuesday, May 15, as part of a two-hour 'Glee' spectacular capped off by the 'Nationals' competition episode. 'Props' is light on song performances but does include Taylor Swift and Jason Mraz covers.

Watch a Behind-the-Scenes of the 'Props' Episode

Watch a Preview of the 'Props' Episode