When a dog sniffs another dog's bottom, they are able to learn about the other dog's sex, age, health, and diet. They can also learn about the other dog's emotional state and whether or not they are a threat.
In addition to gathering information, sniffing each other's bottoms is also a way for dogs to establish social bonds. When two dogs sniff each other, they are exchanging scents that help them to identify each other. This process helps to create a sense of familiarity and trust between dogs.
While sniffing each other's bottoms may seem like a strange behaviour to humans, it is an important part of canine communication. It is a way for dogs to learn about each other and to establish social bonds.