Floating objects

In the Halo 2 there are two places where there are floating objects.

Floating Hat
This happens on the Cairo Station level, after the cinematic rolls, as you descend on the stairwell, you will turn and there will be several SMGs and Battle Rifles. Adjacent to this, is a crate where Sergeant Major Avery Johnson has left his cap. Melee the crate with his cap on it repeatedly. The crate will eventually slip from under the hat, and the hat will be there, motionless. You can't do anything else with it. It's just a minor programming error by Bungie.

Floating SMGs
This glitch can be done on Quarantine Zone (level). Sputnik skull required. Proceed through the level like you normally would, until you reach the Gondola. At the end of the ride, get off and walk to the right until you reach the wall. Grenade jump on the wall and and jump off at the other side. Now you should be in front of the Gondola Sergeant Johnson and Miranda used. Head towards the Index, but before you go through the small corridor where the cutscene starts, there will be two floating SMGs. They shoot at nothing, also if you pick them up they will keep firing. You can be killed by the bullets. They have 60 bullets each in them. Even if you drop them they will keep firing.