Gestures are special animations which players can activate during co-op gameplay. Gestures are contained as separate items in the 'Gesture' slot. There are eight default gestures for both Atlas and P-body, and 8 purchasable gestures.
Performing a gesture during the co-op campaign will at times cause GLaDOS to make a satirical comment upon how much you resemble 'humans'.
Performing gestures also act as criteria for certain achievements.
Air Show Perform 2 aerial gestures before touching the ground in co-op
Asking for Trouble Taunt GLaDOS in front of a camera in each of the five co-op courses
Can't Touch This Dance in front of a turret blocked by a hard light bridge in co-op
Empty Gesture Drop your co-op partner in goo while they are gesturing by removing the bridge under them
Friends List With Benefits While playing co-op, hug 3 different people on your friends list
Gesticul-8 Perform all 8 gestures of your own volition in co-op
High Five Celebrate your cooperative calibration success
Narbacular Drop Place a portal under your co-op partner while they are gesturing
Rock Portal Scissors Win 3 co-op games of rock-paper-scissors in a row
Trivia
The purchasable gestures can be performed using the command "taunt gesturename" in the developer console. This is however, not possible to do when playing with a PlayStation 3 player.
