Dancing Elite glitch
From Halopedia, the Halo wiki
The dancing Elite glitch occurs when an Elite Player model crouches and melees repetitively while wielding a Gravity Hammer, and appears that the Elite is shaking around the place. This can be done in Campaign as Arbiter Thel 'Vadam, Usze 'Taham or N'tho 'Sraom, Multiplayer, Forge and on Xbox Live Matchmaking, particularly in Grifball.
Simply acquire a Gravity Hammer as an Elite, press the Left Thumb Stick and B over and over. From the Elite's perspective, the Gravity Hammer shakes around wildly, but from a third-person view, a laggy, shaking Elite is shown. It is very hard to do this glitch while running or walking, as is crouching repetitively.
This is a sub-glitch, that instead of meleeing, swinging (RT) the hammer (or 7-wood) may make it 'silent' while crouching up and down, it might take a couple of tries. It still has the same properties as a normal swing, but instead no ammo will be lost, and a standard melee 'whack' sound will be heard if in contact with another player, but it will instantly kill. If you aren't the host, ammo will be lost.
This is unknown why this occurs, maybe the Elite model doesn't have a animation for meleeing with a Gravity Hammer while crouching up or down, or both animations overlap each other, using the same model parts such as the Elite's legs, so it shuffles in between the crouching and meleeing animations. This glitch will work with the 7-wood as well, but not with any other weapons.
Or perhaps it has something to do with the Elite's midair melee animation being incomplete. When a Spartan jumps and presses the melee button, he can do a different melee animation from the standard one. When an Elite jumps and presses the melee button, he can only do one melee animation. If the Elite crouches while in midair, he can do two different melee animation. Also, if the Elite crouches and then presses the B button, he will either do a animation where he swings the hammer horizontally, kind of like how Arbiter swings a Fuel Rod Gun and Rocket Launcher, or he'll slam the hammer vertically like a Brute Chieftain does.