Drinking by the Common Boa, Boa constrictor

floor of the oropharyngeal cavity rises, and increasing pressure in the oropharyngeal cavity forces water to the back of the throat and into the esophagus. The expansion and compression stage of the oropharyngeal cavity floor occur in two distinguishable regions. Onset of each drinking stage begins in the anterior throat floor slightly before the posterior throat region, thus setting up front to back motion which functions as a buccal-pump mechanism, acting first to aspirate water into the mouth and then to force the water posteriorly past a sphincter into the esophagus.