Plenty of kissing occurs on Valentine's Day. And most of it will occur with a right tilt of the head. According to a report published today in the journal Nature, people are nearly twice as likely to lean right instead of left when puckering up. The findings suggest that the tendency stems from head-tilting preferences established during the last weeks in the womb.

Onur Güntürkün of Ruhr University in Bochum, Germany, watched lovestruck couples kissing in public places such as airports, train stations, beaches and parks in the U.S., Germany and Turkey. After setting guidelines for a scientifically valid smooch--which requires lip contact, an obvious head turn and a lack of luggage that could influence a person's movements--Güntürkün analyzed 124 kissing pairs. He found that 65 percent of the liplockers tilted their heads to the right.

A similar ratio has been observed for preferential use of the right foot, hand or eye. (Right-handedness, however, is nearly eight times as popular as left-handedness, and may be mediated by different genes or influenced by cultural factors.) Because right head turns are also favored in the final weeks of gestation and among newborn babies, Güntürkün posits that this right bias develops early on and subtly influences behavior long into adulthood.