Watch Taylor Swift and Zac Efron Do a Dance Dare on Betty White, Justin Bieber & Selena Gomez!

The Lorax co-stars Taylor Swift and Zac Efron performed an adorable guitar duet this week on The Ellen DeGeneres Show of Foster the People's "Pumped Up Kicks." They changed the lyrics to the song to be about all the "weird" stuff Ellen DeGeneres makes them do for her show including "dancing on Betty White." So, what exactly did they mean by that?

OK! GALLERY: TAYLOR SWIFT & ZAC EFRON CATCH UP WITH BETTY WHITE & DANNY DEVITO AT THE LORAX PREMIERE

Well, Taylor and Zac decided to participate in Ellen's "Dance Dares," where she asks for videos of people dancing behind people without them knowing. So, at the premiere of The Lorax, the co-stars danced behind some of Hollywood's hottest stars. And the video is nothing short of hilarious.

"We had some moments yesterday that were too good to pass up at The Lorax premiere," Zac explained on The Ellen DeGeneres Show. "So we did a few Dance Dares."

OK! NEWS: TAYLOR SWIFT & ZAC EFRON PLAY A FOSTER THE PEOPLE GUITAR DUET FOR ELLEN DEGENERES

In the clip, Zac and Taylor teamed up and danced behind Betty and Selena Gomez. Betty actually caught Zac in the act, and he ended up having to give her a big hug.

Taylor also did a Dance Dare behind Justin Bieber and Akon!

And, was it just us, or does it look like Selena and Justin Timberlake were in that studio, too? Are they working on a big collaboration? We hope!