Researchers have long used mirrors to gauge self-awareness in animals. (So far, dolphins, magpies, some primates, and an elephant have passed the test.) But mirrors can also test the ability of animals to learn Physics of Light Reflection 101—a different but still impressive achievement that was mastered, most recently, by pigs.
Donald M. Broom and two veterinary students at the University of Cambridge started by letting penned pigs look at themselves and their surroundings in a large mirror for five hours. Then, without the pigs looking, they positioned the mirror so it showed a bowl of food otherwise hidden behind a barrier. Seven out of eight pigs went around the barrier and found the bowl in just twenty-three seconds, on average, showing that they could learn to use a mirror to gather information about their surroundings.
In contrast, nine of eleven pigs that had never before encountered a mirror wrongly looked behind it in their search for food. (The tenth pig just walked around aimlessly, while the last one simply knocked over the food-obscuring barrier.)
Pigs are already known to be pretty smart, and this study neatly confirms it—though it remains to be seen whether they can pass the mirror test for self-awareness. (Animal Behaviour)