The Dancing with the Stars siblings take on Sia and Akon on Spike TV's new series

Credit: Christopher Polk/NBC/Getty

They’re best know for their Dancing skills, but Derek and Julianne Hough aren’t too shabby at lip-synching, either.

In an exclusive preview of an upcoming episode of Spike’s Lip Sync Battle, the siblings make some unexpected – and blush-inducing – choices as they show off their triple-threat talents.

First up, Derek, 29, wigs out in an emotional performance of Sia‘s “Chandelier” (though we suspect DWTS judge Carrie Ann Inaba wouldn’t approve of the lift).

But it’s Julianne, 26, who makes her brother cover his face when she offers up a raunchy take on The Lonely Island and Akon‘s “I Just Had Sex.”

As the good book says, hips don’t lie. And neither do the shocked facial expressions of Julianne’s “straight-up traumatized” big bro and host LL Cool J.

Lip Sync Battle premieres Thursday at 10 p.m. ET on Spike.

How Well Do Derek and Julianne Hough Know Each Other?