Chameleon colors aren’t just camouflage, says Eli Greenbaum, an evolutionary geneticist at the University of Texas at El Paso—they also change due to temperature shifts or emotions. 

“Male chameleons will, in most cases, immediately change colors in response to seeing another male, and in this instance, to itself in a mirror,” says Daniels F. Hughes, a doctoral candidate in Greenbaum’s lab.

See what happens when this male Chameleon notices the “rival male” in the mirror. Things get interesting at about 1:20 on the video.