To unlock Pinhead Bowling, earn 10,000 points in Story Mode. Turn the cheat on and Pinhead Bowling will become available in the Training Mode. This is a fun mini-game that tests your swing kick by allowing you to knock over bad guys (like bowling pins). There are 10 frames in all... and 300 is the perfect score.

Alternately, enter the cheat HEADEXPLODY in the Cheat screen of the Specials menu to unlock the mini-game.