Dogs lap with open pumping driven by acceleration

Dogs lack the ability to form a seal and suck fluids into their mouth like humans, horses, and insects like mosquitos and must drink fluids using other means. They do so by lapping: a rapid extension and retraction of the tongue that brings water out of a bath and into the mouth. In this study, we measured lapping in 19 dogs and developed a physical model mimicking the dog’s tongue to elucidate the fluid mechanism of dog lapping. The results demonstrated that tongue size governed lapping frequency. In addition, it suggested that dogs curl the tongue to create a larger liquid column so they can drink more water each lap. Comparing lapping in dogs and cats revealed that, despite similar morphology, these carnivores lap in different physical regimes: a high-acceleration regime for dogs and a low-acceleration regime for cats.