The physics engine in Halo: CE can be really silly at times. One time I was crossing a bridge (this is the level where you get to drive a Scorpion), and I got to the part where there's a gold Elite on the other side of a short wall. I toss a grenade over the wall. The Elite dodges sideways and dives behind the plasma turret in the corner. The grenade goes off and lifts up the plasma turret. It bounces off the Elite (squashing him flat) and goes over the side.