Demonic Illusion: Hell Viewing Technique
This technique subjects targets to visions of their greatest fear, regardless of whether or not they're aware that they're afraid of it. This "fear" can be something that the target is actually scared of or merely the one image that they least want to see. When Kakashi Hatake uses this technique on Sakura Haruno, he makes eye contact with her as he activates it. Kakashi then seems to disappear in a swirl of tree leaves, leaving behind what Sakura fears: a dying Sasuke Uchiha. Being presented with such a gruesome image, one that, at the time, Sakura believes to be real, gives her enough of a shock that she faints to see it.