The 63-year-old patient came for a routine colon cancer screening with endoscopic technology, which relies on inserting a dedicated camera into the digestive tract.

But the surprise was when the endoscope reached the transverse colon, the long, upper and hanging part of the large intestine, where doctors found a completely alive and healthy fly.

According to the British newspaper "Daily Mail", doctors said that how the insect got alive to this area was a "mystery."

They added that this could be due to contaminated lettuce that the man ate the day before the test was due.

Doctors said that in "rare cases" insect eggs found in fruits and vegetables could survive stomach acid and hatch in the intestines.

The U.S. Centers for Disease Control and Prevention says some infected patients have no symptoms, but others experience abdominal pain, vomiting and diarrhea.