When your
lady is in the "reverse cowgirl" position, you put clench your hand with the middle knuckle raised (similar to the frogging punch). With this protruding knuckle you then place it on her spine and
rub back in forth. The feeling is very intense/ticklish. It
will cause her to moan in a weird fashion and her arms
will become incapacitated past the forearms for a brief moment.
Some women also seem to do weird things with their mouths during the moment.