Medical researchers sent out questionnaires to sword swallowers around the world. The 46 respondents had collectively swallowed about 2,000 swords in the past three months.

25 had swallowed more than one sword at a time; five had swallowed at least 10 at a time; and one person had downed 16 swords at once.

The most common medical complaint was of a sore throat, or 'sword throat' as it's known in the business.

Typically this would occur while they were still learning, after frequent performances, or from stunts involving multiple or unusually shaped swords.

Some reported lower chest pains, often lasting for days. Abstinence from sword swallowing would lead to a recovery.

Sixteen respondents mentioned intestinal bleeding and one was told by doctors that a sword had 'brushed' his heart.

Distractions posed a major health threat to performers. One swallower slashed his esophagus after being distracted by the macaw on his shoulder;

A belly dancing sword swallower suffered a major haemorrhage when a bystander shoved dollar bills into her belt, causing three blades in her esophagus to 'scissor'.

The researchers concluded that "although the risk of sustaining life threatening injury is low for an experienced swallower while relaxed and concentrating on swallowing a single sword, the risk over a career is high."