First a little bit of background. Tihar is the second largest festival celebrated in Nepal. During the five days of Tihar, many animals are worshipped along with dogs including rows (Kaag Tihar), Cows (Gai Tihar), Ox (Govardhan Pooja) and Dogs (Kukur Tihar).
In Hindu mythology, Yama is considered to have two messenger dogs - Shyama and Sharvara, who guard the door of hell. Nepali Hindus believe that by worshipping dogs they are able to see death positively, because a dog follows them in their final journey. By pleasing dogs, they hope to please Yama himself.
Alternatively, some people also believe that Kukur Tihar is just a way for Nepali people to show their appreciation to the man’s best friend. According to ABC Science, dogs might have been first domesticated around the region of Nepal and Mongolia, which tells you just how long people in Nepal co-existed with their doggie companions.