Lower gun

In Halo: Combat Evolved you could create the illusion of lowering your gun by simply aim directly at the ground (this works best when a pistol is equipped). In Halo2 you could press down on the D-pad to lower your weapon. In Halo3 it's a little more complicated than it was in the previous games to lower your gun. In Halo3 you must hold down the following buttuns for four seconds: Left Bumper, Right Bumper, A, Left analogstick and down on the directional-pad. Keep in mind that in Halo3 you can not lower your gun in an online party, such as matchmaking or in a custom game online, but only in a local party or system link.

Trivia

 * Nobody is sure why Bungie removed the option to lower your gun over Live
 * Lowering your gun is usefull when creating Machinima