The authors of the study used high-speed visible light videos and X-ray videos to show that instead of scooping liquid with the back of their tongues as was previously thought, dogs draw liquid upwards into their mouths in a column as it adheres to the dorsal surface of the tongue. (See video)

"We conclude that cats and dogs share the same basic mechanism for lifting liquid from a bowl into the oral cavity and transporting it through the oral cavity: liquid adheres to the dorsal surface of the backwardly curled tongue tip," the study says. "X-ray videos of dog lapping reveal the dexterity with which their tongues trap previously lapped aliquots between the rugae on the roof of their mouths and the dorsal surface of the protruding tongue, in order to access the next aliquot without losing the previously ingested one."

The full-text study of "How dogs lap: ingestion and intraoral transport in Canis familiaris," is available on the website of the journal, Biology Letters.