Dusty Springfield wasn't talking nonsense when she sang about "The Look of Love." The chart-topping blonde with the golden voice belted out scientifically plausible lyrics about come-hither eyes, as studies have shown that our pupils play an active role in signaling attraction. When we spot a comely face, our brains release dopamine, which triggers pupil dilation [source: Murphy]. Thanks to the surge of dopamine in our brains that excites the nerve endings in our eyes, the pupil muscles contract and dilate our peepers [source: Spiers and Calne].
But pupil preferences aren't uniform across the board, and bigger isn't always better. Whereas heterosexual men find women with larger dilated pupils more feminine and beautiful, most straight women opt for medium male dilations that signal sexual interest, but not to a potentially violent extreme [source: Tombs and Silverman]. However, women who tend to engage in short-term sexual relationships with "bad boys" were googly-eyed for the larger pupils as well [source: Tombs and Silverman].