Many agree sexuality is a spectrum (as is gender) and that most people are not entirely homosexual or entirely heterosexual, and a new study reveals very few women who identify as straight are actually completely straight.

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The study was just published in the Journal of Personality and Social Psychology. Researchers from the University of Essex in England and Cornell University in the U.S. looked at 345 women and found women who identify as straight are aroused by images of people from both sexes. They found this by tracking eye dilation and other physiological responses while women were shown videos of attractive men and women, separately. These physiological responses could represent a way of more accurately determining sexuality, as they cannot be consciously controlled.

Women who identified as lesbian in the study appeared to show a much stronger response to attractive women than attractive men, compared to straight women, but straight women showed at least some interest in both. They also found lesbian women do not consistently respond to sexual situations in a more masculine way than straight women do, despite some having suggested that would be the case.

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“Although some lesbians were more masculine in their sexual arousal, and others were more masculine in their behaviors, there was no indication that these were the same women,” said Dr. Gerulf Rieger, of the University of Essex. “This shows us that how women appear in public does not mean that we know anything about their sexual role preferences. Men are simple, but women’s sexual responses remain a mystery.”

This study could show that society encourages people to pick a side—either to identify as gay, straight, or bisexual without any deviation. However, it appears likely some people who identify as completely straight have some inclination toward their own gender.

One of the study authors, Ritch C. Savin-Williams of Cornell, told Vice that similar research suggests men also respond to explicit images of other men to some degree. It's not only women who are identifying as straight and don't fully respond that way.

"There are aspects [of male sexuality] along a continuum, just as we have always recognized with women," she said. "Men have gotten so much cultural crap put on them that even if a man does have some sexual attraction to guys, they would never say it."

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All of that said, some are questioning the legitimacy of these results. A vaginal photoplethysmograph was used to get some of the results, which is a device that measures arousal in the vagina. A Daily Beast writer argues that device could find arousal from many kinds of stimuli. "Straight women’s vaginas proved to be the omnivores of the genital world, responding even to depictions of chimpanzee sex," journalist Samantha Allen wrote. "But this doesn’t mean that straight women aren’t straight any more than it means they are all secretly into bestiality." She essentially said it just means sexuality is very complicated.