The can opener is when you have the mount OR are in his guard, you clinch him just like a Mui Thai clinch and pull his head forward trying to make his chin touch the mat through his chest. If he has you in his guard he'll sit out of it to release the pressure. If he's mounted he'll usually tap, unless he can squirm out of it or counter it quickly.
I'm not sure what the proper name is for the "fist crunch" into the jaw pressure point, but I've had it done to me and then used it myself and it W%@#%! hurts when it's done right.