A study by the University of London found that dogs can capture human yawning. In this study, when a person yawned in front of them, 21 of the 29 dogs yawned, but when people just opened their mouths, they did not respond. The results support the correlation between age and contagious yawning, as dogs with more than 7 months can capture yawns. Dogs are not the only pets that can catch human yawning. Although not very common, after seeing people yawning, they already know that cats will yawn. Infectious dozing of animals can be used as a means of communication. When they saw their mirrors or other fighting fish, usually before the attack, the Siamese fighting fish yawned. This may be a threatening act, or it may be to oxygenate the fish’s tissue before exercise. As part of the courtship ritual, Adley and the emperor penguins yawned each other. Contagious yawning is related to the temperature of animals and people. Most scientists speculate that this is a thermoregulatory behavior that some researchers believe can be used to communicate potential threats or stress situations. A 2010 study of budgies found that yawning increased as temperature increased near body temperature. People usually yawn when they are tired or bored. Similar behavior can be seen in animals. One study found that brains in sleep deprived rats were warmer than their core temperatures. Yawning can lower brain temperature and may improve brain function. Contagious yawning can be used as a social behavior to convey the time of rest for a group.