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When a predator swallows their prey, usually that’s the end of the story. But scientists have discovered an eel that can escape from a fish’s stomach!

This fact was discovered just a few years ago, when Japanese scientists tried putting eels in the same tank as a much larger fish called a dark sleeper. Unsurprisingly, the eels were quickly eaten. But they didn’t stay eaten for long! Some of the eels swam straight back out of the fish that swallowed them.

That story is amazing enough, but the scientists needed to know more. How deep did the eels go into the digestive system? And how on Earth did they manage to escape?

To watch the eels inside the dark sleeper, the scientists fit a fishtank with an X-ray video camera. Next, they gave the eels some dye to make them easy to spot on the X-ray. Finally, it was time to feed the fish.

The scientists were astonished by what they saw on the camera. After being swallowed, each eel went down the esophagus (food pipe), all the way into the stomach. From there, some of the eels managed to escape by going tail-first, back the way they came. Rather than going all the way back to the fish’s mouth, the eels sneaked out through the gills, the slits that fish use to breathe underwater.

These escapes are a race against the clock. The stomach is a deadly place, highly acidic and low in oxygen, so eels only have about two and half minutes to find their way out. Of the 32 eels swallowed, only nine successfully escaped and swam away. Talk about a great escape!