Mongrel dog in the context of "Lady and the Tramp"

The tapetum lucidum (Latin for 'bright tapestry, coverlet'; /təˈpiːtəm ˈluːsɪdəm/ tə-PEE-təm LOO-sih-dəm; pl.: tapeta lucida) is a layer of tissue in the eye of many vertebrates and some other animals. Lying immediately behind the retina, it is a retroreflector. It reflects visible light back through the retina, increasing the light available to the photoreceptors (although slightly blurring the image).

The tapetum lucidum contributes to the superior night vision of some animals. Many of these animals are nocturnal, especially carnivores, while others are deep-sea animals. Similar adaptations occur in some species of spiders. Haplorhine primates, including humans, are diurnal and lack a tapetum lucidum.

A cur was a dog breed used by cattle drovers in England. In the United States, a short-haired dog used in hunting and herding is called "cur-tailed", or "cur" for short.

In modern speech, the term cur is usually used to describe a mongrel dog, particularly if its temperament is unfriendly or aggressive. The term is believed to be derived from the Old Norse kurra, meaning 'to grumble or growl'. In Victorian speech, cur could be used as an insult.