Susan was admitted to the hospital at age 6 months by an aunt for evaluation of failure to gain weight. She had been born into an impoverished family after an unplanned, uncomplicated pregnancy. During the first 4 months of her life, she gained weight steadily. Regurgitation was noted during the fifth month and increased in severity to the point where she was regurgitating after every feeding. After each feeding, Susan would engage in one of two behaviors: 1) she would open her mouth, elevate her tongue, and rapidly thrust it back and forward, after which milk would appear at the back of her mouth and slowly trickle out; or 2) she would vigorously suck her thumb and place fingers in her mouth, following which milk would slowly flow out of the corner of her mouth.