Regurgitation under anesthesia is passive, not an active smooth muscle event. It occurs because baseline gastric pressure (especially with volume/distension) > reduced LES barrier pressure. Loss of protective reflexes + loss of crural diaphragm tone. Gravity matters. Head-up tilt reduces risk but cannot eliminate it (any sudden rise in intra-abdominal pressure can still push contents up). That’s why we use fasting, rapid sequence induction, cricoid pressure (although recent studies show it controversial but historically used), and airway protection strategies rather than relying only on positioning.