The scientists originally thought that the animal was employing its neck like an 8-foot-long drinking straw,

Young handsome man wearing doctor, scientis coat over isolated background clueless and confused expression with arms and hands raised. Doubt concept.

lowering air pressure in its esophagus and stomach and allowing atmospheric pressure to push the liquid up its esophagus. However, after calculating that giraffes are unlikely to be able to generate the pressure differential required to lift water from their lips to their shoulders, they abandoned this notion.

The second clue was a veterinary and medical textbook from 1890 that said cattle, sheep, and other ruminants employ their tongue as a plunger to force water into their esophagus and a YouTube video with a close-up of a giraffe at the Phoenix Zoo in Arizona drinking in a suspiciously pump-like way.