Research has revealed the secrets of kissing.
Humans are hard-wired to favour leaning to the right while kissing romantic partners, an international study by psychologists and neuroscientists has found.
The research, by the universities of Dhaka, Bath and Bath Spa, found that kiss recipients have a tendency to match their partners' head-leaning direction.
Experts built on work from Western countries to investigate kissing behaviours in a non-Western context, including a bias for turning the head to one side.
Their work, published in the journal Scientific Reports, studied 48 married couples in Bangladesh, where romantic kissing is not typically observed in public.
Couples were asked to kiss privately in their own homes, then go into different rooms and independently report back on various aspects of the kiss.
Men were about 15 times more likely to initiate kissing than women, and both partners showed a bias for turning their heads to the right.
Dr Rezaul Karim, from the department of psychology at the University of Dhaka, said: "This is the first study to show sex differences in the initiation of kissing, with males more likely being the initiator, and also that the kiss initiators' head-turning direction tends to modulate the head-turning direction in the kiss recipients."