This is quite funny. Go 2 the level crow's nest then go as you normally would until you reach the big area with all the trucks(where the warthog gets blown up by a plasma grenade). Then kill all of the enemies and instead of goin through the door where the brute comes out of keep ggoing srait. When u get to the end turn look to your right and you will see a marine trying to get in a door with another marine on the other side of the door asking the marine to give him a password. I'll let you find out what he says its helarious.

P.S. they don't cuss or say anything bad....ENJOY!