It's just her hands, and her upper thighs.
The rest diminished, erased, leaving you wanting, drawing with your mental graphite the rest, how you want it to look, act, respond.
It's the absence of those other parts that starts to drive you mad. Your heart rate increases, your pupils dilate, your nostrils flare, until suddenly the civility you use as your mask has come off.
It lies there on the floor, abandoned, forgotten. You will return to it, eventually, but only once you've finished with her.