A new study has found people really do have a "gaydar" - and can judge someone's sexual orientation in a blink of an eye.
The research, published in the Public Library of Science journal, found people were able to judge people's sexuality with above-chance accuracy, relying on no more than "grossly impoverished facial photographs", such as grayscale or hair-removed images, presented for only 40-50 milliseconds.
In the study, 129 US university students viewed 96 photos each of young adult men and women who identified themselves as gay or straight.
The images did not include facial hair, make up, and piercings, as these could give clues.
According to the findings, the sexual orientation of women was easier to judge than men's, with participants 65 per cent accurate when differentiating between straight and gay women compared to 57 per cent accurate for men.