Making eye contact for an appropriate length of time is a delicate social balancing act: too short, and we look shifty and untrustworthy; too long, and we seem awkward and overly intimate. To make this Goldilocks-like dilemma even trickier, it turns out that different people prefer to lock eyes for different amounts of time. So what’s too long or too short for one person might be just right for another. In a new study, published today in Royal Society Open Science, researchers asked a group of 498 volunteers to watch a video of an actor staring out from a screen and press a button if their gazes met for an uncomfortably long or short amount of time (above). During the test, the movement of their eyes and the size of their pupils were recorded with eye-tracking technology. On average, participants had a “preferred gaze duration” of 3.3 seconds, give or take 0.7 seconds. That’s a pretty narrow band for someone on their first date! Making things even harder, individual preferences can also be measured: Researchers found that how quickly people’s pupils dilated—an automatic reflex whenever someone looks into the eyes of another—was a good indicator of how long they wanted to gaze. The longer their preferred gaze, the faster their pupils expanded. The differences are so subtle, though, that they can only be seen with the eye-tracking software—making any attempts to game the system likely to end up awkward rather than informative.