'Project Runway': Uncertain About Their Challenge, the Designers Just Dance (Exclusive Video)

Entering a room full of dancing elders, the Project Runway designers are left a little confused about their next challenge in this week's episode.

"OK, so what's the angle?" asks competitor Amanda Valentine. "Are we making dancing costumes? I've stopped trying to guess, so I'm just going to dance in the meantime."

VIDEO: Heidi Klum, Tim Gunn Spill Secrets on 'Project Runway'

Soon, mentor Tim Gunn arrives to clear up the mystery: They will be creating "a fashionable look for a mature client."

"In the real world, fashion designers work with clients of all ages, and Project Runway is no exception," Gunn says. "Good fashion is both ageless and timeless."

Joan and Melissa Rivers serve as guest judges this week alongside designer Rachel Roy.

Project Runway airs at 9 p.m. Thursdays on Lifetime.