"It's Not You, it's Me: Detecting Flirting and its Misperception in Speed-Dates" is a fascinating approach to the study of flirtation. It uses a machine learning model to parse speed-dating data and detect whether the participants were flirting. Here's a sci-hub link. I found three key insights in the paper.
First of all, people basically assume that others share their own intentions. If they were flirting, they assume their partner was too. They're quite bad at guessing whether their partner was flirting, but they do a bit better than chance.
Secondly, the machine learning model was about 70% accurate in detecting flirtation. It's much better than the speed date participants themselves, despite having far less information to draw upon and the fact that the authors used a more forgiving standard of success for people's detection rates than for the detection rates of the machine learning model.
Thirdly, storytelling and conversations about friends seem to be the strongest signals of flirtation. Talking about the mundane details of student life (this was on a college campus) were the strongest signals of non-flirtation.
Finally, men and women have quite different approaches to flirtation:
Men who say they are flirting ask more questions, and use more you and we. They laugh more, and use more sexual, anger [hate/hated, hell, ridiculous, stupid, kill, screwed, blame, sucks, mad, bother, shit], and negative [bad, weird, hate, crazy, problem*, difficult, tough, awkward, boring, wrong, sad, worry] emotional words. Prosodically they speak faster, with higher pitch, but quieter (lower intensity min). Features of the alter (the woman) that helped our system detect men who say they are flirting include the woman’s laughing, sexual words [love, passion, virgin, sex, screw] or swear words, talking more, and having a higher f0 (max).
Women who say they are flirting have a much expanded pitch range (lower pitch min, higher pitch max), laugh more, use more I and well, use repair questions [Wait, Excuse me] but not other kinds of questions, use more sexual terms, use far less appreciations [Wow, That’s true, Oh, great] and backchannels [Uh-huh., Yeah., Right., Oh, okay.], and use fewer, longer turns, with more words in general. Features of the alter (the man) that helped our system detect women who say they are flirting include the male use of you, questions, and faster and quieter speech.
This paper has changed the way I think about skillful heterosexual flirtation. I used to think that flirting was a unisex behavior, and that men and women were decently skilled at detecting it. In much the same way that it's harder to write a novel than to read one, I thought that the hard part was signalling your own intentions, not interpreting theirs.
Now, I think that a strategy for skillful flirtation is to get the other person to broadcast their intentions, and learn to interpret their signals correctly. Men and women have different flirting styles. Each person knows when they themselves are trying to flirt. But they're bad at guessing when their partner is trying to flirt. This suggests that if you can get your partner to engage in their own natural flirting style, and get good at detecting it, then you can guess their intentions with much more confidence than the average person is capable of.
Both men and women should try to make each other laugh, let their voices be more musical, and provoke each other to talk about love and sex. They should tell stories about their lives and friendships and try to avoid mundane details.
A man who wants to signal flirtation to a woman should ask lots of questions that provoke the woman to talk about herself at length. Note that the "appreciations" and "backchannels" that are negatively correlated with women's flirtation are responses that women tend to give to men who keep going on about themselves. This is the old standard advice.
A woman who wants to signal flirtation to a man should maybe find topics they can complain about together - hopefully in a lighthearted way. She could also talk about her life in such a way that it provokes him to be curious and ask questions about her or observe connections between himself and her.