text:  The National Zoo had trouble for decades. It took the first pair of pandas, the ones that Pat Nixon welcomed around 50 years ago, 11 years just to mate. The female, Ling Ling, experienced multiple pseudo pregnancies. It's exactly what it sounds like when a panda's hormones imitate a pregnancy without there actually being one. And the scientists don't know she's actually pregnant until a baby is or isn't born. A frustrating fake out for researchers.