Golden Retriever

　　Besides fulfilling the function of breathing, the nose is the most sensitive part of a dog's sensory organs. A dog's sense of smell is 1 million times more sensitive than that of a human. The olfactory organ of most mammals is called the olfactory mucosa, located in the upper part of the nasal cavity, with many folds on its surface. When animals inhale air that reaches the olfactory mucosa, it stimulates the olfactory cells, which transmit signals along the densely packed olfactory nerves within the mucosa to the olfactory nerve center, producing the sense of smell.

　　The area of a dog's olfactory mucosa is about four times that of humans, containing approximately 200 million olfactory cells, 30 to 40 times more than humans. Humans mainly observe the environment and acquire information through their eyes, while dogs rely on their noses. Dogs primarily use olfactory information to recognize their owners, distinguish the gender and mating state of conspecifics, recognize routes, directions, prey, and food.

　　When dogs recognize and differentiate things, it first manifests as sniffing behavior. For example, when given food, dogs repeatedly sniff it several times before deciding whether to eat it. When encountering strangers, dogs always circle around to sniff their scent.

　　A dog's sensitive sense of smell mainly shows in two aspects: one is sensitivity to odors; the other is the ability to distinguish odors. Experiments have shown that dogs can still detect sulfuric acid diluted to one ten-millionth. This sensitive olfaction is also a key reason why dogs have become humans' companions in life and work among many animals.

　　Dogs' keen sense of smell has been fully utilized by humans in many fields. Drug detection dogs can find tightly packed marijuana, cocaine, and other drugs among numerous mail packages and luggage.

　　Police dogs can identify and track suspects by detecting scent sources from items, blood stains, sweat, and footprints left at crime scenes. Clothes and shoes worn by a person can still be recognized by police dogs even after being stored for 2 to 3 months.

　　Explosive detection dogs can accurately detect explosives hidden in buildings, vehicles, ships, planes, and other objects. Rescue dogs assist people in locating victims buried deep in snow, sand, and collapsed buildings.

　　However, when a dog enters sleep mode, its olfactory organs also enter a dormant state until it wakes up.