The cat suddenly vomited a lot of undigested cat food.
There are four possible reasons why a cat might vomit a lot of undigested cat food:
1. If a cat eats too much or too quickly, or if the cat food is too hard, it may cause excessive pressure on its stomach and lead to indigestion, which may cause it to vomit undigested cat food.
2. The cat may have eaten spoiled cat food, causing it to vomit due to a foreign object in its body. 
3. If your cat frequently vomits hairballs, this is not normal. In this case, you should help your cat reduce its hair intake. You can do this during shedding season, or regularly brush your cat's fur, and feed them hairball remedy, cat grass, or egg yolks.
4. If you suddenly feed your cat new cat food, it may cause indigestion and vomiting due to the cat's inability to adapt. In this case, you need to mix the old and new cat food together and give the cat a gradual adaptation process.
When you notice your cat vomiting, do not scold or hit them. Take it seriously, as this could indicate a health problem. If you cannot resolve the issue at home, take them to the vet immediately.
