Break the neck of 30 enemies
This is a Metal Gear Solid 2 achievement.

To break an enemys neck, first you need to grab him. Unequip any weapons youre using and approach him from behind. Stop when you get right next to his back (let go of the left analog stick) and immediately mash the shoot button. The soldier will make a noise every time you press it. Keep mashing until you break his neck. If you don't let go of the left analog stick before pressing the shoot button, your character will throw the enemy to the ground, and probably trigger an alert when he gets back up. A good way to stop the enemy is by first holding him up (pointing a gun to his back when really close) and then breaking his neck. Do this to 30 soldiers and the achievement is yours.