The OK Check-In System
The Thumbs Up / Thumbs Down system
In the OK Check-In System, hand gestures are used to communicate boundaries without disrupting the flow of play.
This may be initiated by one player using the OK hand gesture to ask if the other player is OK. A player who is not OK may also initiate by going directly to a response.
Responding with a thumbs-up hand gesture indicates everything is fine and play should continue.
Responding with a thumbs-down gesture indicates that play should stop and the the player should be removed from the situation.
Responding with a flat hand indicates that the player isn't sure how they feel. This should be treated in the same way as a thumbs down.