Invisible grenade throw
From Halopedia, the Halo wiki
Template:Ratings The Invisible Grenade Throw is a special trick on Halo 2 where a player can throw a grenade without their character physically doing so.
Walkthrough
The process is simple. Grab a Sentinel Beam and shoot until it overheats. Then when it is cooling down, throw a Grenade. The grenade will seem to be coming out of you as you cannot see your hand throw it. It also works if you overheat a Plasma Pistol or Plasma Rifle.
Note: This glitch also tends show up during a lagging matchmaking game.