[okie]

There is a pushing pressure against PP#1...but this in turn pulls the piece of string (left arm) straight! It is a below plane pulling of the left arm (unless #3Acc is zeroed out) If you want that stony compression sound you gotta have it. Without it your flying wedges are like a balsa wood shuttle re-entering the earth's atmosphere! It is a beautiful blend of geometry (flying wedges) and physics (extensor action)