When your player gets close to the enemy and the screen flashes, hold E for a speed kill. Do not release the key. When the Prince attacks from behind, the dagger will flash. Quickly press the LEFT MOUSE BUTTON to strike. A speed kill is not one strike, but multiple strikes. The Prince may need to strike from three to five times at an enemy to kill it. However if you do not time the speed kill correctly, the enemy will attack you. In this case, rewind time to try again.