We excluded cases in which injury was related to swallowing items other than swords, such as glass, neon tubes, spear guns, or jack hammers...More at the link, including observations re the technique:
Thirteen respondents did not volunteer any medical information, but 19 described sore throats, usually when they were learning to swallow, after performing too frequently, or when they were swallowing multiple or odd shaped swords. Lower chest pain, often lasting days, followed some performances and was usually treated by abstaining from practice. They rarely sought medical advice. Six suffered perforation of the pharynx or oesophagus. Three of these had surgery to the neck, one having a 1.5 cm laceration at the level of D2 and a pneumothorax, one a pinhole laceration at C6 and surgical emphysema, and the other having a pharyngeal tear. The perforations were treated conservatively in three patients, one of whom had a second perforation with aspiration of a neck abscess after further injury. Three others also had probable perforations, one of whom was told that a sword had “brushed” the heart, and one had pleurisy and another pericarditis after injury, suggesting extraoesophageal trauma. No one underwent thoracotomy, although one had a breadknife removed transabdominally. Sixteen mentioned intestinal bleeding, varying in quantity from melaena or finding some blood on a withdrawn sword to large haematemases necessitating transfusion.
The gag reflex is desensitised, sometimes by repeatedly putting fingers down the throat, but other objects are used including spoons, paint brushes, knitting needles, and plastic tubes before the swallower commonly progresses to a bent wire coat hanger. The performer must then learn to align a sword with the upper oesophageal sphincter with the neck hyper-extended. The next step requires relaxation of the pharynx and oesophagus and particularly the horizontal fibres of cricopharyngeus, which are not usually under voluntary control...For those (few) interested, there is a Sword Swallowers Association International.