You may enjoy the smell of coffee in the morning, but it is not the coffee itself that you are smelling. The human nose can only smell molecules that escape liquid, float into the nostrils, and dissolve into the thin layer of slime coating the olfactory nerves. Stick your nose directly into the coffee, and you will be too busy coughing and sneezing to enjoy the bouquet.

Scientists have long assumed that smelling underwater, like smelling under coffee, was impossible for mammals.

“It was something that mammals couldn’t do,” said Dr. Kenneth C. Catania, a biologist at Vanderbilt University. But Dr. Catania has discovered, much to his surprise, that moles and shrews can do it. They did not evolve a radically new nose, however. They just starting blowing bubbles.

Dr. Catania’s first clues came in the 1980s, when he was a graduate student studying star-nosed moles kept at the National Zoo. The moles hunt for prey underground and underwater. Dr. Catania noticed that when they were underwater, they sometimes released a stream of bubbles, at about two bubbles a second. If the moles were holding their breath, it did not make much sense for them to be leaking.