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Easy Flame Grenadier kills
To easily kill a Flame Grenadier, shoot the fuel tanks on its back. It will then become a very large mobile grenade. Do not stand too close to it or you will be downed or killed.

Skipping cinematics
Press Back to skip the cinematic sequences. Whenever Marcus is talking to control (he will have a finger on his ear) or to Alpha 2, you can also them. Marcus will sometimes say something similar to "Don't wanna here it" or "Quit yapping".

Hidden sequence
When the "Gears Of War: Press Start" screen appears, do not press Start. Allow the game to idle for a few minutes, and a bonus video will begin to play.

Hidden message
Successfully complete the game, and allow the credits to end to view a secret message.

Jack Thompson reference
Enter the arcade room on the "Day One" multiplayer map with a character or the Ghost Cam. One of the fake arcade machines is entitled "Murder Simulator", a jab at attorney Jack Thompson, who often labeled Gears Of War (among other games) a "murder simulator".

Easy "A Parting Gift" achievement
At the main menu, select the "Multiplayer" option, and set the match type to "Local". You can play split-screen, and have the person going for the achievement swing a grenade with LT, but do not throw it. Have the other player down him (not kill him), and stand over his body. The grenade will also drop and kill both players. Do this ten times to get the "A Parting Gift" achievement.

Easy "Around The World, Again" achievement
At the main menu, select the "Multiplayer" option, and set the match type to "Local". You can set the match to one round with two minutes against one bot (or another controller). Then, just win on every map to get the "Around The World, Again" achievement.

At the main menu, select the "Training Ground" option. At the bottom of the list, choose the "Build Your Own" selection. Set the bots to one, difficulty to Casual, and rounds to one with two minutes. Press Start, and then select the map. Win a game on every map to get the achievement. Note: It is easier to play as the Cog team.