There are different reasons that your cat might be throwing up food. Sometimes it's something as innocent as a change in diet, while other times it could be something severe such as a damaged esophagus or perforated small intestine. So, here's a quick primer on some trouble signs to look for.
Undigested Food Covered In Mucus
If your cat is throwing up food that is not digested at all, and it's mainly covered in mucus, than what they might be suffering from is a problem of their esophagus. In this instance, the food has not made it to the stomach. This happens when the cats' esophagus is not capable of transporting the food to the stomach. Your cat most likely won't make a gagging sound that often accompanies vomiting. That's one key sign to differentiate regurgitation from vomiting.
However, don't think that just because the cat acts okay, and might even attempt to eat the regurgitated material, that you can just forget about it. In fact, this can be symptomatic of a serious problem. The esophagus might either be narrowing or widening. Your cat might might end up swallowing food incorrectly and taking food into their air passages and choke. So, you need to bring your cat to the vet and tell them the exact symptoms and let the veterinarian move forward with the appropriate action.
Cat Vomiting Blood
The presence of blood in your cats' vomit can be terrifying. It might be something as minor as a bacterial infection or gastroenteritis or similar irritation, but it could also be an ulcer or a perforated intestine. There is no way to tell without doing a thorough examination. When you see blood in the vomit, you need to contact an animal hospital and immediately set up an appointment. The vet will be able to do an examination and see if there is tenderness in the abdomen or if there is any jaundice around the eyes. They also have machines on hand at the hospital to look inside the stomach to see if there are ulcers or perforations.
Cat Vomit With Bile
Bile can be a sign of an upset stomach due to a change of food. If you have just switched the cat over to a new food, you might want to switch them back and see if the problem subsides. However, bile can also be a sign that your cat has taken in some sort of poison that can have a deadly effect. For this reason, you cannot sit back and let time pass. If you notice the cat acting different, such as walking oddly or exhibiting extreme fatigue, immediately head to a vet.