That feeling of ‘something’s off’ when you’re around certain people starts long before they do anything obviously strange, and it’s because our brains pick up a lot of odd details.
The stare lasts one beat longer

There’s a kind of rhythm to normal eye contact. Look, look away, come back, that sort of thing. It’s part of the reason why it feels weird when somebody holds your gaze for a little longer than expected.
Just a single second longer is all it takes for things to feel a little creepy. It’s not always obvious, and that’s why your conscious mind might not recognize it. But your subconscious certainly does.
The expression doesn’t fit the moment

Pay attention to that person’s facial expression. You might notice that they smile unusually or laugh at unexpected moments. For example, you tell them your dog is sick, and you see the ghost of a smile on their face. It’s not a huge grin, though, that’d be too obvious.Â
It’s something a little more subtle. Still, there seems to be a bit of a disconnect between their mouth and eyes because their expressions don’t match. Your brain notices the difference before you’ve even worked out what’s going on.
They’re observing before they’re joining in

Noticing someone is one thing. Studying them from across the room is something else, and it’s not good. Yes, creepy people pay a lot of attention to who someone talks to and where they sit. They’re almost like hunters in how they watch what other people are doing.
All of that watching comes before they ever say hello, and that’s why it feels so off-putting. It stops feeling like they’re interested in you socially, and more like they’re doing surveillance of you in some way. Perhaps nothing bad is happening. But it’s enough to feel weird.
The coincidences start adding up

Accidentally meeting someone at a random place is totally normal. At least, it is the first time. The second time is still probably coincidental. But by the fourth time, there’s clearly something up, and you have every right to feel a little creeped out by it.
Research on stalking has found that repeated following and showing up around someone are some of the most common forms of stalking. They usually appear as part of a pattern, rather than a single event. Someone shopping at the same grocery store isn’t a big deal, but someone appearing at your coffee shop and gym, too, is more than coincidence.
Everything feels a little too polished

Most friendly people aren’t perfect friends, and they’ll interrupt or miss a joke sometimes. They’re fine to disagree with you sometimes, too. It’s all perfectly normal. But someone who’s always a ‘yes man’ or mirrors everything perfectly is a little strange.
Not all copycats are creepy, of course. It’s usually only the ones who copy your behavior in a way that doesn’t fit the situation. Someone trying too hard to be your friend might have some other motive, and maybe not necessarily a positive one.
Too much precision

Being controlled in your movements is fine, but too controlled isn’t. You know the kind of person we’re talking about. It’s the person who barely shifts in the chair and never makes those little human movements. They don’t tap the table. They don’t shake their leg.
No, all of their movements seem kind of rigid or overplanned, and it’s enough to creep most people out. It makes it seem like all of their moves have been rehearsed beforehand. They probably haven’t, but still, that feeling doesn’t go away.
Their body seems half a second behind

The conversation is moving normally. Yet for some reason, it feels like the other person’s body is buffering, as their reactions come in a fraction of a second too late. They only laugh when the joke’s already gone, for example.
It’s pretty off-putting when someone lacks coordinated head movements. A slight slip in timing, even by a little, can feel off in a way that’s hard to describe. But it’s definitely there, and it’s enough to make you feel a little unsettled.
The face goes blank too quickly

You might notice that their expressions change way too quickly. They’re smiling at you one second, but the next, it’s absolutely nothing. No slow fade or little leftover grin. You simply get a blank face, and it feels like they turned off their expression.
That’s creepy. Real facial expressions usually change over time, rather than stopping dead, so the sudden change can make you feel quite uncomfortable. It might be something tiny, but the suddenness is hard to ignore.
Your name keeps coming back

Hearing your name seems nice the first time. Then it happens again and again. Overusing someone’s name makes it feel like the conversation is too focused on you. There are other people involved in the discussion, after all.
You don’t need someone dropping your name into every other sentence, and when someone does, it could be for a bad reason. They might be trying to create familiarity that isn’t actually there yet. That sure is creepy.
Sources: Please see here for a complete listing of all sources that were consulted in the preparation of this article.