Yeah, I find it weird why the bother doing that in Halo though.

Well it was probably an afterthought, spur of the moment thing.

In Assault on the Control Room I found a glitch.

When you get out on the ground part of the big place where you can usually get the banshee and theres a bridge you have to go over...yeah.

When your there, go to the little ditch where some dead marines and ammo are where the giant fin-like thing that goes up to the control room entrance. Then climb up the fin thing, snipe the hunter sitting there on the left. Then slowly skid down off the right almost on top of the other hunter.

He won't see you, or move towards you unless you touch him.
Its grand for a nice study of the hunter anatomy.