Why she looks at you then looks away

When she looks at you and then looks away, it can mean she's interested, shy, caught off guard, or just glancing at whatever moved. One look-and-away tells you almost nothing. A pattern is more useful: she looks, looks away, and then looks back again, maybe with a small smile, over a few minutes. Even then you're getting a hint, not an answer, and the only way to find out more is a low-risk smile and hello.

That's the practical version of the question people search ("she looks at me then looks away, what does it mean?"). The rest of this covers why a look-away happens, what's worth watching for, and what to do with it.

Why people look away after eye contact

Looking away is normal. It's part of how eye contact works.

In one study, Nicola Binetti and colleagues showed video clips of an actor looking straight at the viewer to 498 visitors to the London Science Museum. 428 had usable data. Each person judged whether the actor's gaze felt too short or too long. The average preferred length of direct gaze was about 3.3 seconds, and it varied from person to person. It was a one-way video with no conversation, so it can't predict a real stranger on a train, but it shows that even in the best case, people look away within seconds. A glance away doesn't have to mean anything.

Here are the usual reasons, none of which you can confirm from where you stand:

Interest, with nerves. She noticed you, felt something, and looked away because holding it felt like too much.
Shyness. Shyer people may look at the eyes less. A 2012 eye-tracking study in PLOS ONE (29 Chinese undergraduates, static photos of faces) found that higher shyness scores went with less time fixating the eyes. It's a small, correlational study on photographs, so it points in a direction and doesn't describe any one person.
Awkwardness. You looked at her while she was looking at you. Neither of you planned it. People look away because holding eye contact with a stranger feels like a mistake.
Courtesy. Many people look away from a stranger to avoid staring.
Nothing. She was looking at the clock, her friend, the barista, the door. You were in the line of sight.

What a pattern looks like

A single glance has too many explanations. Several glances over time have fewer. These are hints worth stacking, the same way you would in signs she wants you to come talk to her:

She looks back after looking away. A return look is more likely deliberate than a first one.
She smiles, even slightly, when she catches you or when you smile.
She keeps showing up in your space. She's still at the next table, or walks past again, with a reason you can't spot.
Her body angles toward you between looks: shoulders, feet, or her chair.
She looks away, then checks whether you noticed. A quick look back right after looking off suggests she's aware of you, though not what she thinks of you.

And some that point the other way:

She looks away and stays turned. Her shoulders, feet and attention all face away.
Her face is flat or tight when you meet eyes, not warm.
She never looks back, or her glance lands on you only when you're moving.
Headphones, a book, or a fixed stare at her phone after a look often mean "not now."

A caveat on every list like this: they're about behavior, not minds. Plenty of interested people give no signs, and some friendly people give many. Signs she likes you vs just being nice goes through the wider picture. Researchers studying conversations between people meeting for the first time found that people tend to believe their partner liked them less than the partner reported (Boothby, Cooney, Sandstrom and Clark, 2018, as summarized by Yale's Clark Relationship Lab). That's about conversations, not glances, and it doesn't prove she likes you. It does suggest that people read their own social performance more harshly than others do, which can shape how you interpret a look too.

What to do with it

You have three honest options.

Do nothing

If you can't tell and you aren't drawn to her, it's fine to let it go. A glance in a train car isn't an obligation.

Smile once

A small, relaxed smile when your eyes meet is easy to ignore, easy to return, and costs you nothing. If she smiles back, you've learned something. If she looks away and stays turned, you've also learned something. How to smile naturally has quick drills. Keep it short and let her set the pace: no staring, no holding the look past a few seconds.

Say hello

If you've seen a pattern, or she smiled back, it's reasonable to walk over and say hi. Something short and easy to decline:

"Hey, I noticed you looking over and thought I'd say hi. I'm Sam."
"Hi, quick hello. I liked your jacket. I'm Sam."
"Hey, sorry to interrupt. You looked like you were reading something good. What is it?"

If she smiles and talks, keep it light. If she answers briefly and looks back at her phone or friends, say "nice meeting you" and go. A no, or a clear lack of interest, ends it. Eye contact when you approach covers how to hold your gaze once you're talking, and trust your gut before you approach covers when to skip it. If she's with friends, approaching groups helps.

Try not to build a story

The look-away is a very short event. It's easy to turn it into a story: she's into me, she's playing games, she's shy. You can't know which one. The same look could come from three different people for three different reasons. What you can do is meet it with something small and clear and let her answer.

What to do next

Count glances before you decide anything. One look means little. Aim for a pattern of two or three over a few minutes.
Practice the smile. Next time someone catches your eye, smile for about a second and look away. Do it ten times this week, in any setting.
Say a simple hello if you saw a pattern. Keep it under ten seconds: "Hey, I'm Sam. I thought I'd say hi."
Decide your exit before you go. "Nice meeting you" is enough. Leave if she gives short answers or turns away.
Write down what happened. If you do approach, log it in Run Game as Success or Rejected and jot a line in the session notes about the look that started it. After a few outings, you'll see which signs turned out to be real.

Sources

Binetti, Harrison, Coutrot, Johnston and Mareschal (2016), "Pupil dilation as an index of preferred mutual gaze duration", Royal Society Open Science. Full text. 498 visitors recruited, 428 analysed, video clips of eight actors, mean preferred gaze 3.3 seconds. Limits: one-way video, no conversation, eight actors.
Wang, Hu, Short and Fu (2012), "The Influence of Shyness on the Scanning of Own- and Other-Race Faces in Adults", PLOS ONE. Paper's page. 29 analysed participants, one culture, static faces, correlational.
Yale Clark Relationship Lab, news summary of the "liking gap" research. Summary page only, no sample sizes. Full paper: Boothby et al., Psychological Science (2018).
The pattern lists above are common coaching advice and our own synthesis, not research findings.