Research by Sunghwan Jung
Animals that drink must transport water into the mouth using either a pressure-driven or inertia-driven mechanism. Cats lap using a fast motion of the tongue with relatively small acceleration (~1g), in which gravity is balanced with steady inertia in the liquid. In contrast to cats, dogs accelerate the tongue upward quickly (~1-4g) to pinch off the liquid column, and thus operate within a different inertial regime. The amount of liquid extracted from the column depends on whether the dog closes the jaw before or after the pinch-off. Our recordings show that dogs start to close the jaw at the moment of pinch-off time, enabling them to maximize volume per lap. In addition, dogs significantly curl the tongue ventrally to increase area in contact with water, which scales with body weight to the 1/3 power. By combining a theoretical pinch-off timescale and observational tongue-weight relation, we found that the scaling of lapping frequency with body weight (frequency ~ weight to the -1/6 power) is the same in dogs and cats.
Example views of a dog drinking.