A dog’s sense of smell is its main communication tool. When a dog sniffs other dogs, they learn about their age, sex, and status. A person’s mood can also be evaluated by how they smell to a dog.
A dog can detect tobacco in “ 27 layers of polythene or locate termites” that no other instrument can detect. They can identify the faintest of smells, even when they’re heavily masked by other scents such as the odour of trace amounts of heroin that have been hidden in pungent aniseed.
There has been much research about how dogs can detect illnesses in humans and in particular various forms of cancer. One of the biggest stories was a study into how they detect ovarian cancer.
Dogs can detect scents we don’t even know exist.
Source: Animal Bliss