Hidden death? Assassinating from a hiding spot. ... Hidden blades.
On a completely unrelated note, I've finally figured out the mystery behind what irks me in AC:2, 'least I think so... The flow of the story. The transitions; as well as some of the many timeskips; don't feel right t' me at times. As every other console AC game doesn't jump around even half as much, I believe that's why I get into 'em more, despite 1 and Revelations not bein' better games overall.