The news from the National Zoo over the weekend has surpassed giant panda fans' wildest dreams: Not one but two newborn cubs made their way into the world Saturday.
The zoo has never had a living set of twins before, and although Mei Xiang is a dedicated mother, raising two cubs requires the care and concentration of an entire team of experts.
Read on for some of the biggest questions about the challenges -- and cuteness! -- ahead.
Q: How is caring for panda twins different?
While Mei Xiang has tirelessly cared for her singleton cubs in the past, panda moms usually aren't as attentive to twins. In fact, pandas won't usually nurse both cubs in the wild -- they'll care for one and allow the other to die.
When panda twins are born in captivity, vets swap the cubs back and forth to allow both to be cared for by their mother. "Our goal is for each cub to spend an equal amount of time with their mother," zoo officials said in a press release.
When one of Mei's cubs is away from her, it's warmed in an incubator and fed a mixture of baby formula, puppy formula and water. The formula is hand-strained to remove any clumps.
Q: Do the twins spend any time together?
Not yet, due to the swapping. The zoo said it's too early to guess when they might be placed together.
Q: How can vets tell the cubs apart?
One cub -- believed to be the second-born -- weighs about two ounces more. That larger cub was the first to be retrieved by vets, who marked him or her with a bit of green food coloring on the left hip.
Q: The cubs are twins, but do they have the same father?
Right now, that's still a mystery. Mei Xiang was artificially inseminated in late April with semen from the zoo's male giant panda, Tian Tian, as well as from Hui Hui, a giant panda living in China.
Zoo scientists will conduct DNA tests to determine the cubs' father or fathers. Zoo spokeswoman Devin Murphy said Monday the panda team hasn't yet determined when those tests will be done.
Tian Tian has fathered all of Mei's previous four cubs, even when she was also inseminated with semen from other pandas.
Q: When can we expect to learn the sexes of the cubs?
Not until the DNA tests are performed, Murphy said.
Mei Xiang's previous four cubs were a male and three females, in that order. Two have survived: male Tai Shan, who was born in 2005 and now lives in China, and female Bao Bao, who celebrated her second birthday just a day after the twin cubs were born.
Q: Are twin pandas common?
Giant pandas have twins approximately 50 percent of the time, but this is only the third time a giant panda has given birth to twins in the United States. "There are only two other female giant pandas who have successfully reared twins and it required a lot of human support," the zoo said on its web site.
Mei Xiang did give birth to twins in 2013, but only Bao Bao survived; the other twin was malformed and stillborn.
Q: Are there any extra dangers with twin pandas?
The zoo is working to ensure that both cubs are well-fed, kept warm and cared for, even when one isn't with mama Mei Xiang. The panda team cared for the smaller cub all night Sunday after they were unable to swap cubs when Mei Xiang refused to put down the baby she was holding. Vets bottle-fed the smaller cub and then tube-fed him or her to make sure the cub was getting enough food, and they say it went well.
However, the mere fact that Mei had twins means zoo vets are able to be more hands-on this time. With past cubs, Mei would hardly ever put down her baby, so the vets were often unable to examine the cubs until they were a bit older. This time around, vets are able to swap out the cubs without upsetting Mei, and can make sure they're healthy.
Caring for newborn panda cubs is always challenging, even with a singleton. "As we've stated, the newborn cubs are vulnerable and this first week is incredibly important and the risk remains high," the zoo said on its website. "Our team is doing great work around the clock and we'll continue to keep you posted."