Mystery solved! Here’s why your cat (sometimes) eats grass

Cats do a lot of weird things. One of the biggies eats grass, often only to vomit it up minutes later. Now, after perhaps centuries of mystery, scientists think they know why.

Researchers surveyed over 1,000 cat owners on the Internet who spent at least 3 hours a day watching and hanging out with their pet. As many cat parents suspected, eating plants is an extremely common behavior: 71% of animals have been caught red-handed at least six times in their lifetime, while only 11% have never been observed in swallowing greenery.

Many online explanations of grass eating postulate that this behavior helps cats vomit when they feel sick. But only about a quarter of grass eaters were observed vomiting afterward, and 91% of those surveyed said their cat didn’t seem sick until it drenched in plant matter.

Instead, vomiting is just an occasional byproduct of weed consumption — not the goal — according to the researchers. Eating plants is instinctual and has an evolutionary advantage for felines — or at least it used to be, they report this week at the annual convention of the International Society for Applied Ethology in Bergen, Norway. Their theory, based on research on chimpanzees and other wildlife, is that munching on grass helps animals expel intestinal parasites (p. 106) by increasing muscle activity in the digestive tract. Except today’s cats probably don’t have these parasites anymore. The authors argue that the strategy likely first evolved in a distant ancestor. (Scientists haven’t tested another common hypothesis: that eating grass helps cats vomit up hairballs.)

The team’s advice to cat owners: Buy or grow indoor grass for your pets to chew on. This will give them a chance to exercise this innate behavior with a safe source of non-toxic plant life. And if your cat vomits afterwards, you can at least take comfort in knowing that it wasn’t on purpose or out of spite…probably.

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