A very long time ago, someone must have witnessed a cat and a dog in a pitched battle. It was probably pretty traumatic. After all, an irate cat can be a whirlwind of shrieking claws. And a dog can be an intimidating adversary when pushed too far.

It must have made quite an impression on some ancient witness.

How else to explain why we're still living with that creaky old — and, as it turns out, entirely inaccurate — expression, "They're fighting like cats and dogs."

Especially since there's little evidence to suggest cats and dogs have any natural enmity towards each other.

In fact, a new study in the Journal of Veterinary Behavior — one that uniquely looks at the relationship between cats and dogs sharing the same home — suggests they get along just fine.

A cat and a dog snuggle under a blanket In most cases, cats and dogs in the same household get along famously. (Photo: Gladskikh Tatiana/Shutterstock)

For the survey, researchers from the University of Lincoln surveyed 748 cat-and-dog households spanning Europe, the United States and Australia. More than 80 percent of pet owners said these classic arch enemies like each other just fine.

A meager 3 percent of respondents said their pets couldn't share the same room.

Sounds a lot like every other relationship, especially when you share the same house — and sometimes have to jostle over the best seat on the couch.

News flash: Sometimes, roommates despise each other.

"We really wanted to know what is it that makes cats and dogs amicable," study co-author Sophie Hall, a co-author on the study, tells The Guardian. "They are often portrayed as the worst of enemies, but that isn't always the case."

Everyone has a role to play

Cats however, did show a little more anxiety around dogs than the other way around, which may be understandable considering the size difference between the species. They were also named, overwhelmingly, as the instigators when conflict did rear its head. The survey respondents noted that their cats were three times more likely to threaten their dog than the other way around. And in fights, it was the cat that inflicted the most damage.

But dogs, so adorably oblivious to the dark machinations of others, would still pick up their toys and show them to cats. In fact, more than a fifth of dogs flashed a "Wanna play?" to cats. But cats, according to the survey, just weren't ... err, feeling it.

Only about 6 percent of cats flashed a toy to a dog.

Those cats probably had their minds on other things. Like how to burrow their way so far under the dog's skin as to effectively cause him to lose his mind — and maybe get shipped out to an asylum far from the household.

This would seem like a good time to direct your attention to a video posted on Reddit this week showing a cat pestering a dog — before the dog finally musters his courage and stands up to his tormentor.

While a cat's patience as a hunter may seem legendary, a dog has his limits — and this case, he even has his day.

But even that conflict, according to the new study, would be a rare exception.

Close-up of dog and cat side by side The divide between cats and dogs seems to have been greatly overstated. (Photo: Jagodka/Shutterstock)

"Owners shouldn't be deterred from having both cats and dogs," Hall notes in The Guardian. "In general, both animals are seen as being really comfortable around each other, which goes against what we might think. We shouldn't think that they can't live happily together."

So maybe it's time to finally retire that old expression, or perhaps tweak it to something like, "They're fighting like people who have lived under the same roof for a long time."

Then again, we're still fond of the phrase "It's raining cats and dogs" — even if we haven't had so much as a tuft of fur fall from the sky in ages.