 Marcel Duchamp’s L.H.O.O.Q. Rasée (1965) is a picture that is perceptually indistinguishable from a faithful reproduction of Leonardo’s Mona Lisa. But Duchamp earlier made another picture (L.H.O.O.Q.) where he drew a moustache and beard on the picture of Mona Lisa. Duchamp’s L.H.O.O.Q. Rasée (as ‘rasée’ means ‘shaven’) is a reference to this earlier picture and we, presumably, see it differently from the way we see Leonardo’s original: the missing moustache and beard is part of our experience, whereas it is not when we look at Leonardo’s original. And it is difficult to see how we can describe our experience of L.H.O.O.Q. Rasée without some reference to the mental imagery of the missing beard and moustache. What is interesting in this example is that the mental imagery of the beard and moustache is influenced in a top-down manner not just by our prior knowledge (about how the world is) but also by our prior art historical knowledge.