It all started when the National Zoo proudly tweeted about the birth of its new baby gray seal pup. Animal lover Sarah Hill, who lives in Virginia, threw down the gauntlet to the Virginia Aquarium, daring the marine institution to offer up it's own cute animal.

The aquarium obliged, responding with an otter in its tank — with an osprey!

And the volleys went back and forth.

Soon the #cuteanimaltweetoff was born. Zoos and aquariums across the country couldn't resist joining the fray.

Even zoos in the U.K. and Canada joined in.

Heck, even the San Diego Symphony joined in, because ... well, why not? When it comes to cute, zoos and aquariums aren't the only game in town.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.