Calories in > calories out is the only way animals and pre-industrial humans managed to wake up the next morning. Having a choice in what you eat or don't is probably one of the greatest accomplishments of our species.

That was a pretty interesting read. I looked to see if I could find more recent info, and it all seems to be coming from the same person, Joseph Dudley. The most recent report of his I found, from 2015, lists 17 cases.

Dudley's first report, the one linked in the Wikipedia article, highlights how much there still is to learn about animals we think we know. Hippos are pretty well studied, yet before the first incident in the 1990s, there was no documentation at all about hippo carnivory.

We can find a number of reports of other vegetarians eating meat, I know I have seen photos and articles of rabbits and deer doing it, but it usually seems to come down to food shortages or other environmental stress, though not always.

From one article on hippo cannibalism observations:

From Nat Geo

David Pfennig, a biologist at the University of North Carolina, Chapel Hill, said that there are certain advantages to eating a member of your own species.

“It’s a perfectly packaged form of nutrients you’re likely to need,” he said.

You reminded me that when I was browsing new releases this last weekend there was some hippo themed movie on the list (Hungry). I looked it up, and while not the Hungry, Hungry Hippos movie that has been in limbo, this one referenced the American Hippo Bill, which sounds like it would have been....interesting...had it been enacted.

(Wikipedia)

House Resolution 23261, also known as the "American hippo bill", was a bill introduced by Representative Robert F. Broussard of Louisiana in 1910 to authorize the importation and release of hippopotamuses into the bayous of the state.

Broussard argued the hippopotamuses would eat the invasive water hyacinth that was clogging the rivers and also produce meat to help solve a meat shortage in the United States. The chief collaborators and proponents of Broussard's bill were Major Frederick Russell Burnham and Captain Fritz Duquesne. Former President Theodore Roosevelt backed the plan, as did the United States Department of Agriculture, The Washington Post, and The New York Times, which praised hippopotamus meat as "lake cow bacon".[6][4] William Newton Irwin, a researcher for the United States Department of Agriculture recruited by Broussard, told Congress that the bill could add one million tons of meat to the yearly American supply, and further suggested that more exotic animals should be imported for the same purpose, including dik-diks, rhinoceroses, African buffalo, Tibetan yaks, and Manchurian pigs.

Although the "American hippo Bill" developed a broad base of support, it was never passed by the US Congress.