The below description is taken from LEGO.com.
If you’ve ever been sure that somebody was silently following you and making silly faces, but nobody was there when you turned around, it was probably the Mime. He shows up in public parks, outside restaurants and in market squares, where he performs routines and does impressions of passers-by without ever making a sound.
No one pretends to be trapped in an invisible box or walking against the wind as well as the Mime does. His best pal is the Circus Clown, and the two frequently join forces to get even bigger laughs and applause from their audience!