What goes through a girl's head when she notices a guy's boner? [possibly NSFW]

I pose this question just for fun. I'm sure it depends on the situation and the relationship between you and the guy, so answer however you want. To clarify I'm talking under the cloths visually noticeable boner. The boner is such a funny/weird thing. All guys have some anxiety about the subject, some more than others, but what do you women think about it? Do you find it funny? Sexy? Scary? Have any stories that can get to the heart of the matter?