It takes 8.2 seconds for a man to fall in love at first sight, say scientists.
What's more, if a man's gaze is more like four seconds, research suggests, he is less than impressed.
But if the eye contact breaks the 8.2 second barrier, he could be in love, say boffins.
However, women treat both hunks and geeks alike, with their eyes lingering on both for similar amounts of time, reports The Telegraph.
To reach the conclusion, researchers used hidden cameras, and secretly tracked the eye movements of 115 students as they spoke to actors and actresses.
They were then asked to rate their conversation partner's attractiveness.
The journal Archives of Sexual Behavior reported that men looked into the eyes of actresses they considered beautiful for an average of 8.2 seconds, but that dropped to 4.5 seconds when gazing at those they rated less attractive.
The female students, however, did not differ in the amount of time they spent looking at the actors.
According to researchers, men use eye contact to seek out fit and fertile mates.