If you've ever placed a mirror in front of your dog, you've probably wondered what she thinks she's seeing (besides a good dog!). Chances are, she doesn't know she's looking at herself.
While dogs are at a disadvantage due to their relatively poor eyesight, very few types of animals have displayed the ability of self-recognition. This comes from the "mirror test," developed in the 1970s by biopsychologist Dr. Gordon Gallup Jr (and which is briefly covered in the book Know It All). The test involves putting animals in front of a mirror after applying a spot of tasteless and odorless dye to their faces. The frequency at which they touched or addressed the spot was noted and compared to samples without a mirror.
Chimpanzees "passed" the test by demonstrating a tendency to recognize the spots on their faces. Very few other species have followed suit. Other members of the ape family—bonobos, orangutangs, and gorillas—have demonstrated this ability as well. Recent studies have also found that some elephants and dolphins have passed the test, too. And that's about it.
Birds, who are famously active in front of mirrors, are almost always responding to what they believe to be an animal of the same species (one exception is the Eurasian magpie). Humans, for what it's worth, are usually unable to recognize ourselves in mirrors until the ages of around 12-20 months—just in time to check on food that gets stuck in those newly developed baby teeth.