Final answer:
Sword swallowers are performers who must learn to relax their pharynx and esophagus in order to safely insert a sword or other long object into their mouths, down their throats, and into their stomachs.
Step-by-step explanation:
The performer who must learn to relax his pharynx and esophagus is a sword swallower. Sword swallowers are skilled artists who insert a sword or other long object into their mouths, down their throats, and into their stomachs without causing injury. By consciously relaxing their pharynx and esophagus, sword swallowers are able to safely perform this impressive feat.