prince of persia: the two thrones

First you need to sneak up on an enemy, either from behind them or above them. If a speed kill is possible you should get a white shimmery effect around the edges of the screen. You then simply attack (I think), and as the Prince takes the enemy out you have to press attack whenever you see the dagger flash or else the speed kill will fail. The guy doing it is a little quick reacting to the flashes, but here's a video showing it .