Several brands of dog food have been voluntarily recalled after several dogs got sick and one dog died after eating “Hunk of Beef Au Jus” dog food, according to Food Safety News. The problem is not limited to this particular brand of dog food, and the FDA has issued an alert about contamination of several different products.

Brace yourselves, because the way it may have gotten into the pet food is pretty grim.

The ingredient that has been found in trace amounts is sodium pentobarbital. You may have heard that name, as it comes up every so often when someone is sentenced to death. It's a barbiturate that forms part of a three-drug cocktail used in executions, so not something you'd want to find in dog chow or your little pooch's kibble treats.

It's a drug that's more commonly used in the euthanasia of pets, including cats and dogs. The FDA warned to look out for signs your pet might be affected by the drug.

"Pets that eat pet food containing pentobarbital can experience drowsiness, dizziness, excitement, loss of balance, nausea, nystagmus (eyes moving back and forth in a jerky manner) and inability to stand. Consuming high levels of pentobarbital can cause coma and death," it said in a statement.

"Any detection of pentobarbital in pet food is a violation of the Federal Food, Drug, and Cosmetic Act—simply put, pentobarbital should not be in pet food."

There are questions over how this drug got into the dog food in the first place. Here goes...

Pet food is made of the parts of animals humans would rather not eat. Only about 50 percent of a cow can be sold for human consumption, according to FDA rules, for example. Slaughterhouses can send the other parts (deemed not fit even for cheap sausages) to a rendering plant, to be ground down by an industrial-sized grinder.

Cows and other livestock aren't the only things that get ground up in these plants, as Slate report. Roadkill, expired meat from grocery stores, zoo animals, diseased livestock (whole) and, you guessed it, euthanized pets can all get ground up in the rendering plant.

Sometimes pet food companies will buy the rendered meat as an ingredient to put into their own pet food.

The FDA is investigating how the drug got into the supply line, but it's possible that it got there because it was present in high quantities in euthanized rescue dogs that were ground up in a rendering plant, and then sent out to be used in dog food.

It's literally a dog eat dog world.

Products affected by the recall include several Gravy Train products, a range of Kibble 'N Bits, Ol' Roy Strips Turkey Bacon and several of the Skippy Premium Chunks range.

A full list of the recalled products can be found here on the FDA's website.