4. Week 4: Switch Up Night

Julianne Hough returns to the show as a guest judge once again. In a change of pace the entire cast opens the show with a wild group dance. Then the contestants switch partners for the competition based on the home audience's Twitter votes. Scores are combined with last week's for next week's elimination. In a special surprise Derek shows off his first choreographed routine for the Macy's Stars of Dance.