In recent years, dozens of people in the United States who bought prepackaged salads at their local grocery stores found unexpected extra ingredients mixed in with their kale and romaine: frogs, lizards, rodents and even a bat.

In 10 instances, the animals were still alive. (Perhaps, that made the encounters less gruesome … or infinitely worse.)

Researchers recently reviewed reports of these animal discoveries dating back to 2003, describing their findings in a new study. They presented 40 examples of bagged salads purchases in 20 states that included unwelcome wildlife stowaways; 38 of these encounters took place during the past decade. [9 Disgusting Things That the FDA Allows in Your Food]

The scientists collected data on incidents that had been covered by news outlets online, noting details such as the date and location of the animal discoveries; the type of produce; whether the produce was boxed or bagged; and the animal species — and if it was dead or alive. For the dead animals, the scientists recorded "whether the animal was whole or partial," they wrote in the study, published online July 20 in the journal Science of the Total Environment.

Geographic distribution for 39 incidents of extemporaneous wild animals found by customers in prepackaged produce items purchased in the U.S. (One frog incident from July 2012 didn't include any specific geographic location.) (Image credit: D. Hughes/M. Green/J. Warner/P. Davidson)Of the animals found in salad, about 53% were frogs and toads, and most of the frogs were in the treefrog group. Around 23% of the salad animals were reptiles, while nearly 18% were mammals and the rest were birds, the scientists reported. Most of the mammals were rodents, but the one instance of a bat in salad — a Brazilian free-tailed bat (Tadarida brasiliensis) found in Florida in 2017 — received significantly more media attention than other animals, likely because bats are known vectors for many diseases that affect people, the researchers explained.

They also noted that animal appearances were three times more common in bags of conventional vegetables than in organic greens.

And though this study focused on animals with backbones, the researchers found "numerous instances" of invertebrate life in packaged salads.

"Pending a thorough review, these may in fact outnumber the vertebrate cases," they wrote. It's also possible that wildlife ends up in packaged salad even more frequently than their findings suggest, as some incidents may have gone unreported or were covered only in print media, which was not included in this study, the scientists added.

Prepackaged salads have surged in popularity since their introduction in the 1980s, and the industry's rapid growth and increasing reliance on automated production pipelines could explain how small, wild animals could bypass safety features and end up sealed inside a salad bag, the study authors reported.

This is the first study to address these recurring instances of small vertebrate wildlife in salad, and "it remains unclear whether these occurrences indicate a food-safety crisis or a complaint against food quality," according to the study. Further observations of the harvesting and production process will be necessary in order to pinpoint when and how the animals find their way into salad bags, and what steps might be taken to keep them out, the authors concluded.

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Originally published on Live Science.