Some researchers have figured it out:
They found that women rated [male] dancers higher when they showed larger and more variable movements of the head, neck and torso. Speed of leg movements mattered too, particularly bending and twisting of the right knee. In what might be bad news for the 20% of the population who is left-footed, left knee movement didn’t seem to matter. In fact, certain left-legged movements had a small negative correlation with dancing ability, meaning that dancers who favored left leg motion were rated more poorly. While not statistically significant, these findings suggest that there might be something to that old adage about “two left feet” after all. One final surprise — arm movement didn’t correlate with perceived dancing ability in any significant way.
And definitely watch the videos. They are truly … inspiring.