Grenade slide

The Grenade Slide is a glitch in Halo: Combat Evolved, in Co-op mode with a partner.

Instructions
To do this, you need a partner, a grenade, and room to run. Start running and have your partner watch you. Throw a grenade, and as you throw the grenade, you will slide across the floor. After you throw it you will resume running. You cannot notice this by yourself, as you cannot see your own legs in this game.

When Bungie made the animation for throwing a grenade, they also animated the lower half of the body standing still, so while you are still running, it is not animated as such. A similar glitch occurs when you throw a grenade from a passenger seat of a Warthog or Scorpion tank, with the player standing up inside the vehicle to throw a grenade.