Seeing we're on a nostalgia trip on Halo 3, I thought I'd post this part from the end of The Ark. (I posted this before over on HBO back in 2010).
So at the end of The Ark, there's a ring with a bunch of jetpack brutes and a Brute Chieftain in the middle. I'd always just opened up on them right away, anxious to end the level. Well, as it turns out, the Chieftain is actually shouting at you, challenging you to a duel. He yells, "“For the Prophets! Fight me! I’m right here!”
So if you accept his duel, you and him will fight to the death with the other brutes jeering you.
It's a pretty cool scene, and one that's easy to miss. The wail of the jetpack Brutes when I slew their Chieftain in solo combat was glorious. If you're replaying, I highly encourage you to accept his challenge.