When one is performing coitus on a pregnant female from the rear, one tapes knives to his hands while the female isn't looking. Then one flips the female on her back and using his "knife hands" proceeds to rip the baby out of her. The man is now cover in blood and has rudimentary claws and is presumably in Boston, well not really.
A coked up midget told Josh Landes all about the Boston Crab.
When a man hunches over a woman and eats her out, though from behind. That is, she's lying on her stomach and he's crouched over her back, pulling her legs up, naturally, to eat her out more easily. She may or may not be wearing a Mexican wrestling mask while he does this.