This is a very interesting article.
http://www.sciencedaily.com/releases/2011/01/110103110357.htmEven Healthy Cats Act Sick When Their Routine Is Disrupted
ScienceDaily (Jan. 4, 2011) —
Healthy cats were just as likely as chronically ill cats to refuse food, vomit frequently and leave waste outside their litter box in response to changes in their routine, according to the Ohio State University study. Veterinary clinicians refer to these acts as sickness behaviors.
The researchers documented sickness behaviors in healthy cats and in cats with feline interstitial cystitis, a chronic illness characterized by recurring discomfort or pain in the bladder and often both an urgent and frequent need to urinate.
Edit to add:
There are numerous great articles about animal behavior, including this:
http://www.sciencedaily.com/releases/2009/07/090713121348.htmHouse Cats Know What They Want And How To Get It From You