The man's best friend usually has a wet nose and many dog lovers believe in the myth that wet nose is a sign of a healthy dog. However, it has been revealed now that the slimy surface of a canine nose is actually behind their sophisticated sense of smell.

MRI images of a dog's nasal passages were studied by Brent Craven, from Pennsylvania State University and a team, in order to find how air traveled through them. The team reports, "Damp mucus on a dog's nose 'pre-sorts' smells by blocking the passage of some odor particles more than others."

The team also found that nerve cells at different points along the airways picked up different types of molecules.

The dogs' extreme ability to smell has been brought to use by experts earlier to trace cocaine and even cancer, which has been backed by scientific trials.

As compared to humans, dogs have many more nerve cells in their nasal passages and also a great variety of receptors that pick up different chemicals.

"We've shown that the sorting out of the different odorants before they even get to the receptors is also important," said Doctor Craven.