When you plant your first kiss on St Valentine's Day tomorrow, chances are both you and your partner will turn your respective heads to the right. Not many people know that and fewer still ever worried about it, but the subject was deemed sufficiently important for a leading science journal to publish it.
A kiss is just a kiss until a researcher decides to look at it more closely and produce a study. The result, published this morning in Nature, represents yet another example of our collective, lifelong preference for "right-sidedness".
Humans have a proven preference for turning their heads to the right rather than the left starting from a few weeks before birth and continuing for six months afterwards, writes Dr Onur Güntürkün of the Ruhr University of Bochum, Germany.
This movement isn't just chance, he says. It is thought to influence the later development of visual and motor preferences in the growing child, something that clearly is carried forward into adulthood.
He decided to test the idea in the field, risking the possibility of being labelled a voyeur in the process. "I observed kissing couples in public places (international airports, large railway stations, beaches and parks) in the United States, Germany and Turkey," he writes.
Dr Güntürkün was picky about the pecks he recorded. Head-turning direction was recorded for a single kiss, with only the first being noted, he said. There were also a number of criteria needed before any kiss was counted. Lip contact was mandatory, subjects had to be face to face and they were not recorded if they held anything in their hands in case it might "induce a side preference".
He noted the head-turning preferences of 124 "kissing pairs" and right-turners predominated by two to one. "As the couples come from a biologically adult age range, this result indicates that adults have a head-turning bias towards the right side, just like embryos and newborns," writes Dr Güntürkün
Making more use of the right foot, eye or ear also follows this two-to-one ratio, he said, but this is not dictated by whether you are actually right-handed. Right-handedness is much more common than left-handedness with a ratio of eight to one.
Knowing this doesn't do anything extra for a kiss, but it might be important for the way the brain handles movement, sight and thinking.