Higher Weapons
From Halopedia, the Halo wiki
In Halo 3, lower your weapon (right bumper, left bumper, left stick down, A, d-pad down simultaneously), and get in a Warthog. When you get out, your weapon will be higher than usual and it will not move(like as in it's frozen in it's spot on your screen), until you shoot. This glitch is incredibly easy if you know how to lower your weapon.
