A team of oceanographers watching a deep-sea rover’s camera never saw this coming: a young gulper eel performing fluid acrobatics for the lens.

The reactions caught on video from the group of scientists watching the gulper eel were priceless; at one point all of them oohed as the eel blew up like a black balloon.

“Big gulp! The Nautilus team spotted a gulper eel (Eurypharynx pelecanoides) doing just that in Papahānaumokuākea Marine National Monument,” wrote the team on the Nautilus’s website.

The gulper eel’s mouth can suddenly expand like a soap bubble to allow it to scoop up much larger prey, although the fish is thought to eat mainly small crustaceans. It’s theorized that, because of the fish’s tiny teeth, its ability to stretch to bizarre proportions is more of a back-up plan if food gets scarce and large fish are all that are on offer.

After inflating itself, the gulper—also known as a pelican eel because its scoop-like feeding method resembles the large water birds—abruptly deflates its mouth and swims away. Very little is known about these creatures that live up to 6,000 feet deep: why one might inflate and deflate itself like that, for instance. But new observations of another gulper eel, this one in the Gulf of Mexico, have some researchers speculating that the behavior happens when the fish feels threatened.

The gulper eel in the video is likely a juvenile, the researchers said, given its small size. Adults can reach 3 feet.

Nautilus Live is the brainchild of Robert Ballard, discoverer of the Titanic’s final resting place and a National Geographic Explorer-in-Residence. Follow the live expedition on Twitter.