Panda bears are notoriously difficult to breed in captivity. There's only a small window of a few days each year that the  females can conceive, and both sexes seem more interested in sleeping and eating bamboo than doing anything else. At the National Zoo, they have an additional problem:

Just because they are able to mate, though, doesn't mean they will. Mei Xiang and Tian Tian are what David Wildt, head of the Center for Species Survival at the National Zoo, calls "behaviorally incompetent."

"Tian Tian tries really hard, and is very diligent in his duties," he says, "but he's just not able to pull Mei Xiang into the proper mating position."

The pair is not alone. Of pandas in the United States today, only two, Gao Gao and Bai Yun at the San Diego Zoo, have been able to breed naturally. 

So what does "incompetent" panda sex look like?

As she has in the past, Mei Xiang flopped on her belly like a pancake when she met with Tian Tian—the opposite of good mating posture, which would have her rigid on all fours—and Tian Tian went about his usual routine of stomping around and standing on her, clueless what to do.

After multiple attempts, the keepers ushered the tired pair back to their separate yards.

Things are looking up for horny pandas, though, and years of hard work by a global network of researchers is paying off with behavioral training, panda porn and physical monitoring that might improve future breeding attempts. [Smithsonian]