Dead Elite glitch
From Halopedia, the Halo wiki
The dead Elite glitch is a glitch in Halo 3: ODST in which the dead Elites are "revived" for a short time.
Find one of the dead Elites in found in Mombasa Streets. Have one player stand above the Elite. Have the other player kill the one standing above the Elite. Repeat until a pile of grenades dropped from the player being killed is noticeable. Once a pile of grenades is formed, have a player throw an active grenade into the pile. The whole pile should explode, resulting in the Elites standing up straight, appearing as if they are holding guns, though their hands are empty.
The Elites are never encountered as enemy types throughout ODST, but some of their code is still in effect. As the grenades explode, the Elites will stand because they have no advanced ragdoll code.