That is to say, the fact that the upper level of Lacan’s formula of the analyst’s discourse is the same as his formula of perversion (a-$) opens up a possibility of reading the entire formula of the analyst’s discourse also as a formula of the perverse social link: its agent, the masochist pervert (the pervert par excellence), occupies the position of the object instrument of the other’s desire, and, in this way, through serving his (feminine) victim, he posits her as the hystericized/divided subject who “doesn’t know what she wants.” Rather, the pervert knows it for her, that is, he pretends to speak from the position of knowledge (about the other’s desire) that enables him to serve the other; and, finally, the product of this social link is the master signifier, that is, the hysterical subject elevated into the role of the master (dominatrix) whom the pervert masochist serves.-Slavoj Zizek, "Jacues Lacan's Four Discourses"
In contrast to hysteria, the pervert knows perfectly what he is for the Other: a knowledge supports his position as the object of his Other’s (divided subject’s) jouissance. The difference between the social link of perversion and that of analysis is grounded in the radical ambiguity of objet a in Lacan, which stands simultaneously for the imaginary fantasmatic lure/screen and for that which this lure is obfuscating, for the void behind the lure. Consequently, when we pass from perversion to the analytic social link, the agent (analyst) reduces himself to the void, which provokes the subject into confronting the truth of his desire. Knowledge in the position of “truth” below the bar under the “agent,” of course, refers to the supposed knowledge of the analyst, and, simultaneously, signals that the knowledge gained here will not be the neutral objective knowledge of scientific adequacy, but the knowledge that concerns the subject (analysand) in the truth of his subjective position.