In this game hot girl is giving you a head. the purpose is to avoid cumming. Pressing Z presumably causes some pain around the guy's head, which causes the vertical bar to rise and the excitement meter to fall. When the vertical bar (the pain bar) fills, you die. The idea is to keep a balance between the two bars so you don't cum and dont die. Keep it up long enough and you end up with a row of numbers across the top of the screen, click them and you can get the girl to do anything she would normally do. Enjoy!