A sloth's umbilical cord can be a lifeline for its young in more ways than one. When giving birth, it can stop a slippery newborn from falling right out of the tree, sort of like a natural bungee cord.

A rare glimpse of just such an incredible moment was recently caught on camera in Costa Rica, by local guide Steven Vela.

Pulling over to merely observe a brown-throated sloth (Bradypus variegatus), he and his vehicle of tourists instead bore witness to the late stages of sloth labour.

Seconds after birth, a newborn sloth can be seen suddenly slipping out of its mother's arms and falling, saved only by its umbilical cord.

Dangling from this last tenuous connection, the mother then scoops her infant up and begins cleaning it, at a remarkably un-sloth-like pace.

"A three toed sloth having a baby in the wild is something that you don't see every day," Vela noted on his Facebook page afterwards.

And he's not wrong. Three-toed sloths are generally shy and hard to find in the wild. Coming across one right as it's about to give birth is about as lucky as it gets - that is, if you're excited about sloths.

Rebecca Cliffe is definitely a fan. She's the executive executive director of the Costa Rica-based Sloth Conservation Foundation, and she told CNN that these events are very rare. In fact, she's one of a lucky few who have witnessed similar events.

During he own research, Cliffe actually watched a sloth give birth just a few metres away, except this time, when the newborn fell, the umbilical cord got tangled in a vine.

The baby was ultimately fine, she said, but this sort of thing is probably not the norm. Sloths usually put their arms behind them in preparation for giving birth, as the video below shows; an umbilical cord 'save' is probably a last resort.

"I don't think [hanging from the umbilical cord] happens in every case," Cliffe told National Geographic.

"But I suspect it's quite common and doesn't really cause a problem. Just makes everyone watching a little nervous."

Judging by the squealing in Vela's car, we know she's right about that one for sure. Welcome to the world, little baby sloth!