The mirror test is a measure of self-awareness developed by Gordon Gallup Jr in 1970. 
The test gauges self-awareness by determining whether an animal can recognize its own reflection in a mirror as an image of itself. This is accomplished by surreptitiously marking the animal with two odourless dye spots. The test spot is on a part of the animal that would be visible in front of a mirror, while the control spot is in an accessible but hidden part of the animal’s body. Scientists observe whether the animal reacts in a manner consistent with it being aware that the test dye is located on its own body while ignoring the control dye. Such behaviour might include turning and adjusting of the body in order to better view the marking in the mirror, or poking at the marking on its own body with a limb while viewing the mirror.
Animals that have passed the mirror test are common chimpanzees, bonobos, orangutans, dolphins, elephants, and humans. Initially, it was thought that gorillas do not pass the test, but there are now several well-documented reports (such as on gorilla, Koko) of gorillas passing the test. Human children tend to fail this test until they are at least 1.5 to 2 years old – mirror stage – . Dogs, cats and 1 year old children, for example, usually react to a mirror in fear or curiosity, or simply ignore it, while birds often attack their own reflections.