- Guscon
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- Exalted Mythic Member
They are like little thinks about the game. For example in Halo, on Assault On The Control Room there is a place where, if you stand, you can hear a little peice of piano music. Also the talking Grunt on The Maw. I think there is a good list on halo.bungie.org. If you want to find them, just look around the game, on every difficulty. The Skulls (skulls that have an effect when you pick them up, such as make your HUD dissapear) are mostly found on legendary and only in Halo 2.