Enlarge (credit: Paul Asman and Jill Lenoble)

If you passed out at a party and someone drew a mustache on your face, you’d know it when you next looked in a mirror. There are a few other species—including great apes, dolphins, and corvids—that are also able to recognize themselves in the mirror. Mostly, though, other animals won’t try to rub of any hand-drawn mustaches, because they don’t seem to understand that they’re looking at themselves. Puppies, for instance, have a hard time figuring out this whole reflection business.

Rhesus monkeys are one species that doesn’t pass this test—spontaneously. A paper in PNAS this week describes how to teach them to earn a passing grade. The result raises some important questions about the test, and it could help in understanding what mental tools need to be in place before any individual can recognize their own reflection.

Pranking animals for science

Researchers have been playing the mirror trick on animals for a while to test which species have self-awareness. The thinking is that only an animal with a sense of itself as an entity will be able to make the link between itself and the face it sees in the mirror, and such an animal will rub at any marks they see via their reflection. Because of this, the assumption has been that the species that pass the mirror self recognition (MSR) test have self-awareness.