Looking like "the cat that's got the cream" takes on a whole new meaning when the cat might be suffering from an upset stomach and diarrhoea.
Just as an inability to digest dairy products can cause uncomfortable symptoms in some adult humans, feeding your cat milk can leave it with a funny tummy - and you with a mess to clean up.
Researchers have discovered all mammals - including cats - lose the ability to digest milk efficiently as they develop, due to a drop in levels of the enzyme lactase, which breaks down the sugar lactose, found in milk. Levels of this enzyme are highest in newborn mammals fed solely on their mother's milk - but drop away as the animal starts to eat solid food.
In the western world, the prevalence of a gene for "lactase persistence", bred into the population after the domestication of dairy animals, means many adult humans can digest milk. It is much rarer in Asian populations - and unknown in domestic felines.
If an animal's digestive system does not have enough enzyme to break down lactose, the sugar passes undigested straight through the small intestine to the large intestine.
There, bacteria get to work on it, causing cause cramps, gas and diarrhoea - making for one unhappy kitty.
Sam Boston, pet advisor for Bombay Petfoods, which manufactures the Jimbo's brand, says it's a case of "nature knows best".
"In the wild, cats do not drink milk after they have finished weaning - they have no nutritional need for it once they are on solid food. Some even develop lactose intolerance symptoms because of this," Boston says.
"Some house cats do get fed milk as a treat, or even regularly, but there is no nutritional reason why it should be part of their diet."
If your cat seems to be able to tolerate small amounts of dairy without getting an upset stomach it's probably not doing them any harm - but go easy on the servings. Boston says water is the best drink for cats, plus a diet which provides them with hydration through their food.
"We recommend feeding cats raw meat - it is what they are naturally designed to eat, and is high in moisture to help keep them well hydrated."
Just like humans, adequate hydration is vital for the healthy functioning of your cat's body. The Cornell University College of Veterinary Medicine says water helps cats regulate body temperature, digest food, eliminate waste and lubricate tissue, and allows salt and other electrolytes to pass through the body.
Cats should be provided with clean, fresh water at all times and the water should be changed at least once a day; felines tend to be fussy about stagnant water.
While newborn kittens need their mother's milk or a specialised kitten-milk replacement formula to grow, once they are past 8-10 weeks old it makes sense that feeding them milk from another species, such as cow's milk, won't necessarily agree with them.
The composition of milk from different animal species varies widely, with cats' milk having much more fat than cows' milk. Interestingly, the fattiest of milks comes from whales and seals, which are almost half fat, while human and monkey milks are high in carbohydrate and rabbit milk is high in protein.
So why does the storybook image of the happy cat and her bowl of milk persist?
Well, while cat owners will agree their pets are smart, that doesn't mean they're experts on nutrition. Cats are attracted to milk and cream because they love the taste of the fat - without thinking about the longer-term digestive effects. Sound like some humans you know?