A group of marine biologists off the coast of Australia tagged a healthy great white shark. Then, a few months later, the tag washed ashore. When researchers analyzed data from the tag, they were confronted with a mystery that was deeply weird, and slightly terrifying.

In this video, we learn what the researchers found on the tag. A few weeks after tagging, the shark appears to have been abruptly dragged down into a deep ocean trench, then eaten. The tag remained in the digestive system of the animal that ate it for several days. Whatever animal it was seemed to be bobbing to the ocean surface once in a while, though it never plunged as deeply as it had after it ate the shark.

What kind of deep-dwelling alpha predator did this? Obviously it's very possible that the shark's tag was eaten, but that still leaves us wondering what could bite a hunk off a shark, then zoom down to an incredible depth and back up again? This video is a reminder of how little we actually know about shark behavior and deep sea life.