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pump stroke diagram

The intake stroke draws fluid into the cavity or mouth, while the discharge stroke pushes it out into the esophagus. 

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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.