This is a neat glitch to get inside secret areas or get through a level in under 15 minutes. To do it, just take a warthog to a door (a ghost might work, too) and make it at an angle in which you get out on the side the door is on. Now line yourself up with the door, and get out. Eventually, you'll fall through the door, or through the ground. (if you fall through the ground, you'll go through the celing.) If you miss, get out, punch the warthog, and try again.
Submitted by: Thor