I haven't checked this in awhile; thanks, all, for contributions!
How interesting that a P Professional has adding the carrot stick as phase 4! I like that a lot, since it precludes banging the chin with snap!
Also, I realize that I erred in calling the "thunk" a phase 4: phase 4 is in fact swinging the rope horizontally back & forth with the whole arm, from the shoulder. That does cause the snap to move back & forth & perhaps hit the chin.
So the thunk is beyond phase 4, which there isn't in PNH, except that in this case there is: it's the downward snap of the arm after a half-circle of the rope for momentum, causing the snap to thunk the rail, as per video instruction.