From a distance, garden eels look a bit like some strange grass waving on the sea floor. That’s until they abruptly shrink back into the holes they’ve burrowed in the sand.

The eels seem to be unique among fish. They are capable of swimming free, which they do to change burrows. But mostly, they live sessile lives, anchored in their narrow burrows even when they emerge to feed, like tethered snakes striking at zooplankton too small to see.

In the Red Sea, they live in colonies of hundreds or even thousands, from shallow waters of 13 feet or so, to depths of 180 feet.

When they rise from the sand en masse, their appearance can seem like something from a science fiction movie. But what has recently captured the interest of scientists is what they do once much of their body is waving in the current.