[12 piece bucket]

Something perpendicular must be at a precise right angle to another line or plane but need not necessarily itself be vertical; something vertical is always at least roughly at right angles to the ground, the floor, or the horizon.

Ok Ok . . . So the motion is Vertical Hammering. But that motion must be made Perpendicular to the Left Arm to satisfy the Left Arm Flying Wedge and maintain the Law of the Flail.

For those about to ROCK . . . .