Confusing the Jackals
When you're nearing the brig where Keyes and co are being held prisoner, you can have some fun with the two Jackals pacing up and down the corridor outside. Having made yourself temporarily invisible with the active camouflage found in the earlier empty brig, go right up to the Jackals and whack one or something. They get terribly confused and alarmed, which is a whole lot of evil fun to watch. And you can always tag them with plasma grenades of course! Conveniently there's a checkpoint just as you approach the Jackals, enabling you to revert for more fun time and time again.