Small dogs such as Chihuahuas were also used as living heating pads during illness or injury. Small dogs such as Chihuahuas were also used as living heating pads during illness or injury. Some believe this practice is where the idea of pain being transferred to animals from humans originated, which gave way to rituals such as burning the deceased with live dogs, such as the Techichi, to exonerate the deceased human's sins. Chihuahuas as we know them today remained a rarity until the early 20th century; the American Kennel Club (AKC) did not register a Chihuahua until 1904. As in other breeds with large protruding eyes, Chihuahuas are prone to eye infections and eye injury. The eyes may water in response to dry air, dust, or airborne allergens.