From Wikipedia: The performer must first lean the head back, hyper-extending the neck, and relax the upper esophageal sphincter (a generally involuntary muscle which contracts the top of the esophagus). Retching must be controlled while the sword, lubricated by saliva, is inserted through the mouth and past the pharynx.
Once past the pharynx and sphincter the sword passes swiftly, assisted by gravity, straightening the flexible esophagus. The stomach, at an angle to the esophagus, is brought into line as the sword enters through the cardiac opening. Some swallowers consume a large meal or drink water before performing to give the stomach a more vertical orientation, allowing for easier passage of the sword. Careful focus is required to complete the process without injury, as the sword passes within millimeters of vitals such as the aorta, heart and lungs.
my compliments--never gave it much thought because I have never actually seen it. Your answer was certainly better than what I offered. Excellent work and my apologies to Efficient Admin for not researching the issue.
No problem Larry. I did the same thing - didn't research it and I thought you had a good answer. I thought there was a trick to it, like a retracting sword but as Rachael pointed out, it's more complicated than that and really incredible!