When someone fists you and opens their hand, then that person will then make movements with their hand like a puppetmaster while you follow the handmovements with your limbs.
When you fuck a girlin the ass. Then she reaches into her own vagina, and strokes your dick with the skin in between her asshole and vagina. (Imagine what your fingers look like inside a hand puppet and you'll get it)
n. A male patient who is turned into a hand puppet during a hernia exam when his doctor crams his or her hand all the way up inside, totally inverting the scrotum.