Air swimming
From Halopedia, the Halo wiki
Air Swimming is a phenomenon that occurs when an enemy is killed by a grenade explosion and their body gets stuck between two terrain objects. When the body is too large to fit in between the boxes, it ends up hovering above them, looking as though it were trying to swim through the air. The event occurs most commonly with Jackals.
In Halo: Combat Evolved, when bodies are propelled by explosions, they will sometimes appear to be "frozen" if they hit an object mid-flight; this can also make them appear to be swimming. On a related note, when a Jackal or a Grunt is killed by an explosion, its corpse may appear "wedged" within a metallic structure, floating above the floor.
