Both dogs and cats and ferrets have two anal glands measuring between 1 and 3 cm in diameter under the skin, one on each side of the anus (in the internal sphincter), which function as a calling card to other dogs. These glands are sacs-that contain a yellowish-brown liquid with a very unpleasant odor, which is excreted through ducts that open outside the anus. When a dog is healthy, the evacuation of the liquid occurs naturally with the feces, and this liquid informs other dogs of its sex, diseases, temperament, etc. That is why dogs 
usually sniff each other's behinds when greeting. Another function of the liquid contained in the anal glands is territory marking: the dog marks the space it occupies so that other dogs can smell it and identify it. Additionally, the liquid expelled by the perianal glands also serves to lubricate the anus during defecation.