Why is my cat throwing up undigested food?

Undigested food coming up in a cylindrical, sausage-like shape is regurgitation, not true vomiting. The food never reached the stomach; it came back up the esophagus before digestion started, which is why it looks intact. The most common cause in cats is eating too fast. A slow-feeder bowl, a flat plate or a puzzle feeder all force a slower pace and usually resolve it. If you’re switching foods, slow the transition to 10 days or more, since rapid switches also produce regurgitation in some cats.

When to call a vet: if regurgitation is frequent (multiple times a week) or your cat is losing weight, that points at the esophagus rather than the stomach, and warrants a vet visit.