All players stand in a circle facing each other. One person starts by pulling a grimace and showing it only to the person on their left. That person 'takes on' the grimace, shows it to the whole group, then invents a new grimace and shows it only to the next person on their left.
The pattern continues around the circle: receive privately, display publicly, invent new, pass privately.
This warm-up loosens up facial muscles and inhibitions.