NO!!!

You do NOT crush the back of the neck! You put a long screw-driver, ruler, pencil, anything sturdy and strong, and you pull the tail UP. Crushing the neck will be a very painful death

The most humane way is CO2, though. It knocks them out instantly, no tail yanking, neck crushing... You can get cans of it at WalMart, or Krogers. In my opinion, I think that is the safest way to pre-kill.