Have you tranquilizer gun ready and fire at the target. Get close the sleeping target and go into your crouch position. An icon should appear to wake the target up. Press [Action] to wake your target. When he or she is about to wake up, position yourself at either side or the back of the target. Aim your gun and Snake should hold-up the target. This is an easy way to do CQC and knife kills if you want to get the Assassin's Creed emblem and costume.