Why do guys lift their eyebrows at girls?

This is actually a really common flirting signal. There are all sorts of articles online that talk about all the flirting body language signal, and raising the eyebrows, or the eyebrow flash is on pretty much all of them. The eyes may give away other signs, like eye contact. Are they glancing at you from across the room. To they look from one eye to the other and then down? Also, their pupils often dilate around somebody they like.