"They initially interpret the image as another pig," says lead author and animal welfare scientist Donald Broom. One swine even broke the glass poking at his reflection.

But soon most pigs learned to correctly assess the mirror’s properties, as the subsequent test showed.

The animals were placed in a pen with a bowl of food hidden behind a wall and a fan dissipating the smell all over the room so that the treat could not be tracked. The bowl, however, could be seen in a mirror. Seven pigs out of eight correctly interpreted what they saw and went straight for the prize, spending less than half a minute in doing so. The eighth started searching for the bowl behind the mirror.

The cognitive skills needed to pass this test 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 team has reported their findings in the current issue of the journal “Animal Behavior”.