In the 2013 movie Philomena, an unwed teenage mother is forced to give up her toddler for . Many decades later, she enlists the aid of a journalist to help her find her grown son. When they discover that he died of AIDS, Philomena says she always knew he was gay.

Some people claim to have an uncanny ability to detect the of another person from subtle cues. This kind of is often called “gaydar” (a combination of “gay” and “radar.”) However, skeptics dismiss gaydar as nothing more than a set of stereotypes about homosexuals that are largely untrue.

Canadian psychologist Nicholas Rule studies social intuitions—the snap judgments we make about people we’ve just met. In a series of experiments, he and his colleagues tested people’s abilities to judge others’ sexual orientation, and came to the conclusion that gaydar is real. And the way it works tells us a lot about the nature of social intuitions in general.

When we encounter new people, we quickly size them up. For example, we know almost instantly what their is. And we’re generally quite accurate, because most people clearly advertise their in terms of hair style, clothing, and mannerisms. We’re even pretty good at judging the sex of a person from quite some distance.

We’re also accurate when it comes to judging race or based on multiple physical characteristics, such as skin tone, facial features, and hair quality. However, prior expectations play a significant role in race perception. Take, for example, the case of Rachel Dolezal, the white civil-rights activist who pretended to be black—and even served as president of a local chapter of the NAACP.

For a humorous take on errors in race perception, watch the Saturday Night Live sketch, “The Day Beyoncé Turned Black,” in which wealthy white people when they learn their beloved singer is African-American.

Within seconds of meeting a person, we’ve already assessed their gender, race, age, social class, and many other personal characteristics. We also have a sense of whether we like the person, and whether we can trust them. Our social intuitions work rapidly, and they’re fairly accurate, although they’re far from foolproof. Rule claims that gaydar is just like other social intuitions.

But how exactly does gaydar work? In their research, Rule and his colleagues found four sets of nonverbal cues to sexual orientation they labelled the four A’s: adornment, actions, acoustics, and appearance.

Adornment refers to the way people dress and do their hair, and it’s a social cue that people use to advertise their sexual orientation and also their sex, social class, and even ethnicity. For example, homosexual men tend to be more meticulous about their clothing and hairstyle compared with heterosexual males. But judging people by their adornment alone only takes you so far. After all, the metrosexual style of fine clothing and expensive coiffures is sported by young urban professionals regardless of their sexual orientation.

Action cues are based on the mannerisms people exhibit while they move. Research participants who watched 10-second video clips of people moving were able to judge the sexual orientation or the person in the film at a rate above chance. In a process known as gender inversion, gay men tend to sway their hips like straight women, while lesbians tend to swagger their shoulders like straight men. But again there’s an important caveat: The judges were right more often than not, but they still made many misattributions.

Acoustics refers to nonverbal speech cues to sexual orientation. Rule notes that many people hold speech stereotypes about homosexuals, such as the belief that gay men lisp when they talk. Research doesn’t support this stereotype. Nevertheless, people are good at discerning sexual orientation from the voice of the speaker. Again, we see that gaydar works like other social intuitions, in that the stereotypes people consciously hold don’t match the features their intuitions detect at an level.

Appearance refers to facial characteristics. People shown pictures of faces for as little as a tenth of a second are better than chance at assessing sexual orientation. In fact, accuracy doesn’t go up even when the judges are allowed to look at the pictures for as long as they’d like. This is also true when the faces are cropped so that all cues of adornment (clothing, hairstyle) are removed. However, when people were asked to think carefully about their judgments before responding, their performance dropped to chance, showing that conscious can interfere with the processing of social intuitions.

The fact that facial features provide visual cues to sexual orientation lends support for theories that attribute homosexuality to prenatal experiences such as exposure to in utero. After all, clothing and hairstyle are clearly conscious choices, and mannerisms are often learned, even if unconsciously. However, the shape of the nose and the mouth, which seem to be the pertinent cues, are determined by the way that are expressed early in life, even before birth.

Nevertheless, even action cues to gender inversion, such swaying hips and swaggering shoulders, appear early in life. Judges who watched home videos from people’s could determine their sexual orientation as adults. This suggests that some gender-specific mannerisms may have an epigenetic source as well. So it seems quite likely that Philomena could have known that her little boy was gay, as she claims in the movie.

Furthermore, people differ in their gaydar abilities. People with strongly expressed homophobia aren’t very accurate at judging sexual orientation, even though they think they are. Straight people who have gay friends are more accurate in their judgments, but they feel less in their assessments. And not surprisingly, gays and lesbians are generally quite accurate at judging sexual orientation.

In sum, gaydar really is a thing, in that people are generally good at perceiving sexual orientation from nonverbal cues. However, it isn’t a special talent. Rather, gaydar taps into the same “people sense” we use to quickly size up those we encounter in our daily lives.