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Above left: Disassembled mannequins lying on shelves inside the 'Your Self' storage facility. Above right: A partially assembled mannequin in Gumb's basement (indicated by the arrow).
One of the things that Clarice sees upon entering Lecter's storage unit is a shelf on which are lying some disassembled mannequins. The presence of these mannequins 'in' Starling's unconscious (as represented by the storage unit), relates to the fact that the killer Buffalo Bill (Jame Gumb) has partially-assembled mannequins in his basement (e.g., the one shown in the above right screencap, on which is hanging Gumb's incomplete 'suit' of skin)). This suggests that there is a psychological connection between Starling and Gumb, in addition to the 'physical' connection whereby she is trying to gather information about him.
Recall that the goal of Clarice's analysis is for her to become a fully-grown, sophisticated woman, i.e. a complete woman. But, doesn't Gumb himself also want to become a woman, by putting together his suit? He is assembling it piece by piece, until he has obtained a complete suit that he can wear. In his own eyes, when he accomplishes this, he will have become a woman; but of course, in reality, he will not have become one.
This is, in fact, the psychological connection between the two characters, Clarice Starling and Jame Gumb. Clarice wants to be a complete, authentic woman. As opposed to this, Gumb cannot, can never, be an authentic woman. He is inauthentic - he is trying to become something he is not, something he cannot be. For Clarice to become an authentic woman, she must defeat that within herself which is inauthentic; she must defeat that within herself which cannot be. Gumb represents the incomplete woman within Clarice. That is why she must kill him: She must defeat the incomplete woman within herself, so that she can finish the process of becoming a woman.
Recall Lecter's statement to Clarice in Memphis: "I’ve read the case files, Clarice, have you? Everything you need to know is right there in those pages." The file, though it is physically the one for Buffalo Bill, also here represents Starling's own case file - the file of her psychoanalysis. When she stops trying to 'figure out' the overt clues (anagrams, etc), that is, when it is no longer necessary for her to do so, then her mind is 'freed up' to have the necessary revelation, which occurs when she sees the dress in Frederica Bimmel's closet: her unconscious 'recognizes' the masked clue that Lecter 'embedded' in her mind in the Memphis scene - "Simplicity", the name of a dress manufacturer.
[If you are only interested in viewing the explanation of the film's hidden plot, continue on to part 20 of the analysis. Otherwise, use the buttons below to navigate the analysis.]