Just looking at a cat’s vomitus cannot determine whether it is feline plague. Cats suffering from cat plague will vomit incessantly and have diarrhea, will not eat, drink, and have no energy. If the owner is worried that his cat is infected with cat plague, he can Take it to a pet store for testing. Cats vomiting green water may be caused by indigestion, vomiting hair balls, gastric acid, etc. If the cat is in a normal state of mind, can eat, drink, and is energetic, the owner can observe it for another 1-2 days.