The intake stroke draws fluid into the cavity or mouth, while the discharge stroke pushes it out into the esophagus.
Courtesy of The Physics Teacher
The process repeats, bringing more and more water into the esophagus. The giraffe raises its neck at some point, allowing gravity and the wave-like muscular contractions known as peristalsis to direct water into its stomach.
The researchers estimate that the giraffe can pump water at a speed of 6.7 mph, enough to overcome the pressure from the water already stored in the esophagus and prevent it from rushing back out.