University of Georgia are recording the activities of cats using a collar camera in the aid of wildlife conservation

WE know cats aren't telling us what they get up to. It's something about the look in their eye when they settle down to sleep on your clean laundry pile.

We know they're naughty: those little gifts dropped on your pillow late at night attest to that.

And we're always being told by cat-skin-hatted conservationists how evil they are.

Now, we have an irrefutable insight into the kitty underworld.

University researchers put 60 pet cats in Athens, Georgia, under close surveillance.

Small video cameras provided by National Geographic have opened a window on just what our cats do all day when they slip between your feet and through the door to spend the day - or night - in the suburban jungle.

More than 2000 hours of footage was captured - exposing the murky politics and dark deeds of what we think are little more than lazy lap-warmers.

Don't ever think your relationship with a cat is monogamous, the study found.

"One of the most surprising things we witnessed was cats adopting a second set of owners," author of the study Dr Kerrie Anne Loyd wrote. "Four of our cats were cheating on their owners by visiting other peoples homes and receiving snuggles and food."

But the kitty crimes the cameras uncovered were shocking.

"We found that cats don't bring most of their prey back to their house," Dr Loyd said.

But killer kitties are in the minority: The researchers found that about 30 per cent of the cats under surveillance were successful hunters - stalking down, on average, two animals a week.

Unexpectedly, birds were not their favourite targets.

Instead, cats most commonly caught reptiles. But they were the least likely prey to be proudly presented to owners.

In fact, most bodies were left at the scene of the crime. It was only rare that the cat would think of its owners and return with a gift.

When presented with the hard evidence, the cat owners were shocked.

"It was clear that she was under the deck of my house and had a bird," cat owner Evet Loewen told Mother Jones.

"I stopped watching because I knew what the end point was, that the bird wasnt going to live. I was very upset with my cat."

But the footage did reveal one upside.

Cats shackled with a cat bib and bell were still able to stalk and engage in kitty politics, but were unsuccessful in their hunts.