Scientific principles play out in real life, sometimes without you even realizing it.
One of my cats has been pretty ill for a few weeks now. She had a vomiting episode, and then just pretty much stopped eating. She's always had what I would call a "sensitive tummy" but has otherwise been pretty healthy. So I was convinced that she was a likely victim of inflammatory bowel disease (IBD) and that it had finally caught up to her.
When she stopped eating, we took her to the vet immediately, where she was given an anti-nausea medication and some fluids. We scheduled a "GI Panel" - a special blood test that looks at the functions of the pancreas and tests vitamin levels to look at overall digestive functioning. Abnormal results can often be an indicator of IBD or other health problems that might lead to loss of appetite such as B-12 deficiency or pancreatitis. Her bloodwork came back "boringly normal" but the symptoms remained. It got to the point that all she would it was small amounts of chicken baby food. The vet recommended an ultrasound to look for other signs of inflammation of the intestines, which we scheduled as soon as we could.