"Because the olfactory nerves in the nose are covered with mucous, odorant molecules are all water soluble," Catania said. "So, when these bubbles come into contact with an object, it is almost inevitable that odorant molecules will mix with the air and be drawn into the nose when the bubble is inhaled."
Just because the moles are getting whiffs of interesting odors underwater doesn't necessarily mean they smell them. So Catania devised some additional tests.
One of the complicating factors was the star-nosed mole's unusual nose, which is ringed by a star-shaped set of fleshy appendages. It uses its star like a super-sensitive set of fingers to identify objects it encounters while burrowing and swimming. So, at the same time it is sniffing at an object it is also fingering it with its star.
To determine if the mole can identify edible objects by sniffing alone, Catania created underwater scent trails leading to food and recorded how well the moles' could follow them. To keep the moles from using their tactile star, he put a grid-work between the animals and the scent trails. The openings in the grid were too small for the star appendages to squeeze through but large enough so the air bubbles could pass without difficulty.
These trials demonstrated that the moles could follow the scent trail by sniffing alone (without the tactile star).
Five moles were tested on earthworm scent trails and followed the trail to its reward with accuracies ranging from 75 percent to 100 percent accuracy. Two moles were tested with fish scent trails and followed them with 85 percent and 100 percent accuracy.
When the grid was replaced with a screen with openings too small for the air bubbles to pass through, however, the moles' performance dropped down to the level of chance the same as their performance with no-scent trails.