Having worked with cats a lot, I can confirm that some common symptoms of health issues can be easy to miss. Especially if you're not too familiar with the cat in question. Watching for subtle changes is important, as it can help you catch diseases like FIP cats early.
For example, a sick cat may stop grooming as often. If your cat's fur starts to look messy or greasy, it could be a sign of illness.
Another thing you should watch for is changes in temperament. If your cat starts hiding or becomes less playful than usual, it might not be feeling well. Cats often try to hide their discomfort, so these changes can be subtle. If you notice your cat isn't as active or is avoiding you, it’s worth keeping an eye on.
Lastly, changes in appetite can also be a clue. If your cat suddenly eats more or less than usual, it could be a symptom. The same goes for changes in how much water they're drinking. Keeping an eye on these details can help you catch potential issues early.