Hugh Hefner knew it, and now science has proven it - men like to look at women arching their backs.
But what's new to science could be that women do too.
Researchers in Portugal had 82 men and women hooked up to eye-tracking software while they looked computer-generated 3D models of women in different poses.
The more each model's back was arched, the higher both sexes rated its attractiveness, the study found.
"Increased curvature increases the perception of attractiveness," says lead researcher Farid Pazhoohi of the University of Minho.
In September, Kiwi entrepreneur and former Playboy bunny Sandra Costa told The AM Show the number one rule for girls at the Playboy Mansion was to always bend backwards.
"You had to bend backwards, and the girls were always complaining their backs hurt... If you bent forwards, you'd get demerits. You were never allowed to bend forwards."
The eye-tracking software used in the study found both sexes spent more time looking at the models from behind, than the side or front. Men spent most time on the hips, while women tended to focus on the waist.
"The perception of attractiveness and visual attention to the hip region suggests that lordosis or the arching of the back might signal human females' proceptivity or willingness to be courted," says Dr Pazhoohi.
"This also might explain why women wear high heel shows and why wearing high heel shoes increases women's attractiveness."
The study was published in journal Evolutionary Psychological Science.