Play Bow

WhenScout & Angus want to play, they let the other know with play signals, which they use to get play started and to keep it going. These signals are  aimed at keeping play safe by telling the other that intentions are playful. It also communicates that even if the behavior to follow involves biting, chasing, shaking, or slamming into one another, it is playful in nature. 
Scout is the play bow, - getting down on her elbows with her back end higher than her front end. Abrupt -  the suddenness of the movement is part of the signal as well.