Crysis 3 - Clever Girl

This is best obtained on Mission 2: Welcome To The Jungle.

You will come up to a door that will trigger a cutscene in which you will see the Ceph(aliens) for the first time in the game. These stalkers are more predictable than later in the game. Sneak to the other end of the room and make sure to stand right next to the wall or they will see you. When it passes go up and assassinate.