3. Irene Adler's Safe Code
If there's any woman who has ever got Sherlock hot under the collar then it is Irene Adler. You will remember Irene as the naked one from series two. She certainly knows how to make an entrance and she even succeeded in getting Sherlock a little smitten. But there was more to her nakedness than initially met the eye. This was her way of giving Sherlock the code for her safe. As she told John before climbing out of the window, it was her measurements. This deduction is chosen, purely because it makes Sherlock seem almost human. He may be a sociopathic genius but he still notices the figure of a woman. This is also true for Sherlock's deduction, later in the episode, that Irene Adler was aroused by him and it wasn't all for effect. This seems impossible to know but Sherlock reveals that he could read it via her pulse.