South American horned frogs from the genus Ceratophrys are known as Pac-Man frogs for a reason: their ginormous mouths. 

It's an anatomical perk that opens up a range of dining options denied to other frogs: pretty much anything that will fit inside their mega-mouths is up for eating. Rodents, lizards, crabs, small fish ... heck, even their own kind. But once through the mouth, how does such a supersized meal (sometimes almost as large as the frog itself) even fit? 

That's a question for Dr Thomas Kleinteich from the Zoological Institute at Kiel University in Germany, who made a pretty fascinating discovery recently while working on a research project investigating the "sticky characteristics" of amphibian tongues.

"[B]esides [having to] overcome and capture large prey items, it is critical for these frogs to fit large and bulky prey objects into their body cavity," Kleinteich notes in a paper in the journal Salamandra.

As part of his research, Kleinteich has been generating 3D computer models of amphibians from museum specimens using a micro-CT scanner, which is designed for investigating smaller objects. While scanning a 70mm female specimen of the Argentine horned frog (Ceratophrys ornata), Kleinteich spotted something unexpected it its digestive tract: another frog.

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The prey frog is shown in pink. Image: Dr. Thomas Kleinteich, Kiel University

The unlucky amphibian had been swallowed head-first, and was positioned with its head in the tail end of the horned frog's abdomen. "With the micro-CT, I am able to show, for the first time, how such a large catch can even fit inside a horned frog," says Kleinteich.

After the scans, Kleinteich went on to dissect the frog and was able to remove the prey from its digestive tract, tentatively identifying it as a juvenile northern leopard frog (Lithobates pipiens). At 43mm, the leopard frog was over half the length of its cannibalistic captor.

And it seems possible that this ambitious meal was the reason for the horned frog's demise. Kleinteich notes that the condition of the specimen suggested that the frog had died shortly after it had consumed its prey. "Although the exact cause of death of the predator cannot be reconstructed without any doubt, it might be possible that swallowing this relatively large prey specimen proved lethal in the end," he writes.

Don't you hate it when your eyes are bigger than your stomach?

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Image: Dr. Thomas Kleinteich, Kiel University
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Image: Dr. Thomas Kleinteich, Kiel University