Sometimes we meet a complete stranger and it can feel like we’ve known them forever, that you somehow just 'click'.
When you've only just met someone, of course it's unusual to feel like you could already finish off their sentences, but now it seems science has recognised this sense of having an instant rapport – and there's a simple sign to show if it's happened to you.
Research published in the Proceedings of the National Academy of Sciences this year by a team at Dartmouth college, set out to study the science surrounding why we click with some people and not others.
"Clicking is one of the most robust metaphors for social connection," the study's authors explain. "But how do we know when two people 'click'?"
The research team asked pairs of friends and strangers to talk to each other and rate their perceived connection.
Interestingly, the results showed that for both friends and strangers, the speed in response was a robust predictor of feeling connected.
The study involved 66 participants who took part in 10 conversations, each with a different partner of the same gender.
They were allowed to choose any topic of conversation while the exchange was being videoed by the researcher.
Participants watched the video playback and rated how connected they felt moment-by-moment during the dialogue.
Researchers found people were more likely to feel a stronger social connection if response times during the conversation were shorter.
Members of the first study were invited to come back to their close friends and repeat the experiment.
While close friends rated conversations higher than strangers, response times still determined moments where they felt more strongly connected.
In a third study, participants listened to audio clips of conversations where the response times between speakers had been manipulated.
Again, third party observers felt speakers were more connected when their response time was faster rather than slower, the researchers found.
This suggests a person's response times are a powerful indication of how socially connected they are to someone else, in other words how quickly you reply to a person can be a sign of 'clicking' with someone.
“We’ve all had the experience of clicking with some people but not others," explains one of the study's authors Emma Templeton, from Dartmouth College.
"We wanted to see if something in people’s conversations reveals when they click.
“Our results show that the faster people respond to each other, the more connected they feel.”
Senior author Professor Thalia Wheatley added: "It’s well-established that, on average, there’s about a quarter of a second gap between turns during a conversation.
"Our study is the first to look at how meaningful that gap is, in terms of connection.
“When people feel like they can almost finish each other’s sentences, they close that 250-millisecond gap, and that’s when two people are clicking.”
So why do we click with some people and not others?
Lee Chambers, psychologist and wellbeing consultant says clicking with someone is a feeling that is hard to describe.
"You might be introverted or be in a conversation topic you know little about, but you feel like you've clicked with the person in a way you just can't forget," he tells Yahoo UK.
"The words they use resonate deeply, and the rhythm of your speech feels like a dance, matching step-by-step. The conversation flows like a waterfall, no boundaries or obstacles stopping the flow."
Chambers says clicking is a form of "interpersonal synchronisation" where body language and spoken words match in synchronisation, with the other person’s body language mirroring what you are feeling in a way that feels like they are in your mind.
"Even our brain activity can synchronise, with the same neural pathways activating," he adds. "That feeling of clicking is like our brains coupling together. It requires focused attention and a connection of voice and body language. But when it does happen, we get a feeling that is hard to describes and feels somewhat magical."
It isn't the first time the phenomenon of 'clicking' has been analysed.
In a 2018 study, 42 volunteers watched short video clips while scientists measured their brain activity.
The scientists had previously mapped everyone’s social network, noting who was whose friend, who was a friend of a friend, who was a friend twice removed, and so on.
Results revealed the brain activity while viewing the clips was “exceptionally similar among friends”.
“But that similarity decreases with increasing distance in the social network,” psychologist Thalia Wheatley of Dartmouth College, who led the study, told Greater Good Magazine.
In other words, friends were most similar in their patterns of neural activity, followed by friends of friends, and then friends of friends of friends.
Those neural patterns, Wheatley said, suggest that “we are exceptionally similar to our friends in how we perceive and respond to the world around us. You 'click' more with friends than with non-friends, which fits with our intuition that we resonate with some people more than others. There seem to be neurobiological reasons for that.”
If you're still unsure whether or not you've actually 'clicked' with someone, a 2018 study, published in the journal Psychological Bulletin, found that people behave in specific ways when they’re attracted to or are 'clicking' with someone.
The top signs include initiating conversation, wanting to be in close physical proximity and mirroring the other person’s behaviour.
So if you spot any of these signs it's likely you've 'clicked' with someone.
Watch: What are the different types of attraction?