Miss Piggy, the famed porcine muppet, knew a thing or two about mirrors. In fact, she was seldom without one. She may have been vain, but she was also one smart pig, given that researchers regard the ability to use a mirror as evidence of complex cognition. Now, it turns out, Miss Piggy isn't the only clever porker. Real pigs also understand the value of their reflection, according to new research, putting them in an elite group of animals.

A team of animal welfare scientists at the University of Cambridge in the United Kingdom placed eight domesticated pigs (Sus scrofa), two at a time, in a pen with a mirror for 5 hours. Because pigs are social, they prefer having a companion in a pen; plus they could also observe each other's actions and movements in the mirror. At first, the pigs studied their reflected images and movements; some grunted at their image, and one banged the mirror so hard with its nose, it broke the glass. "They initially interpret the image as another pig," says lead author and animal welfare scientist Donald Broom. That's a classic error that most species never get beyond.

But soon, the pigs showed their smarts. During their 5-hour sessions, they learned to correctly assess the mirror's properties--to understand the relationship "between their own movements and their image in the mirror," including the surrounding environment, says Broom.

Those talents showed up when the scientists later placed each pig in a new test area that contained a food bowl hidden behind a solid barrier. The pigs could see the reflection of the bowl only in the mirror. An overhead fan circulated the food's scent so that the pigs could not simply sniff their way to success. In less than 25 seconds, seven of the pigs correctly interpreted the bowl's image, turned away from the mirror, and ran to get the prize. The eighth pig looked behind the mirror for the bowl.

The pigs' ability to use a mirror is more than a circus trick, the researchers say. It is also an indication of "assessment awareness," says Broom, meaning that they understand the "significance of a situation" and their position in it. Thus, to use the reflected image to find the food bowl, the pigs had to remember what they saw in the mirror, as well as understand the reflection and their movements in relationship to it. Such cognitive skills are an indication of "some degree of self-awareness," says Broom. "It's not conclusive, but it is likely they are self-aware given our results."

The scientists attempted to further verify that pigs are self-aware by giving them the classic mirror-mark test--placing a visible mark on them--to see how they would respond. Unlike most other mirror-smart animals, Broom says, the pigs "paid little attention" to these smudges, "probably because they often get marks on themselves."

Still, the pigs' success in the mirrored food-bowl test means that they should now be added to a select list of species--elephants, dolphins, magpies, gray parrots, some primates, and humans--that can use mirrors, the researchers report in the current issue of Animal Behavior. "Finding sophisticated awareness" in pigs "will hopefully lead to better welfare for them," says Broom.

The study's findings are "very significant," says Marc Bekoff, a cognitive ethologist at the University of Colorado, Boulder. They "extend the range of animals who are self-aware," he says, a mental ability that is necessary if one is to behave in a sentient rather than machinelike manner.