What do i do once i have a halo 3 SILVER skull in my hands in the game?

[Amalio G]

i picked one up. once i picked it up, wat do i do with it?

 

[Bob N]

all u do is drop it and it will be unlocked

 

[barrelchick]

You hit the bad guys with it basically, then after you finish the level press X at the menu and see what the skull is. It's probably one of the special skulls such as grunt b-day or something.