His gaze softens as he draws closer to you. With one hand around your waist and the other cradling your jaw, he pulls you in. You look into his eyes, and notice his pupils have grown large and hungry.

So the story goes in every other romance novel, where enlarged pupils are commonly enlisted as imagery to indicate sexual arousal. And it's not unusual to read advice online suggesting dilated pupils are a sure sign someone you like also likes you back.

But what does the science say?

In fact, it's true: our pupils really do tend to grow large when we're aroused. Here's why.

What is the pupil?

The pupil is an opening in the iris (the coloured part of the eye) which directs light through the eyeball and onto the retina.

Typically this opening is 2-4 millimetres in diameter in bright lig

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