Scars
I know that Ann's remark that Graham could tell her anything personal "as long as it isn't something gross, about a childhood scar" (or similar) is just to indicate her fastidiousness and probably a certain distaste for the human body.
However, I find it an interesting link with 2 of Spader's other films: "Crash" (where scars are part of the attraction and acquiring more in further crashes is part of the sick game) and "Secretary" (where he loves Lee and that includes her self-inflicted scars).