A man in Missouri in the US has left doctors scratching their heads after finding a fly crawling deep inside his intestines.
The 63-year-old patient had visited doctors for a routine screening for colon cancer where they inserted a camera into the intestine, known as a colonoscopy, the Daily Mail reported.
The process continued as usual until the doctors reached the transverse colon - the upper part of the large intestine - where they found a completely healthy fly.
Doctors say it is a 'mystery' as to how the bug got there, but it could be from contaminated lettuce the man ate the day before his appointment.
The patient was questioned after the discovery but admitted that he did not know how the bug got into his body. He didn't feel any symptoms.
He told the doctors that he had only drunk plain water the day before his colonoscopy, as needed to cleanse the intestinal tract.
The evening before his 24-hour fast, he had eaten pizza and lettuce - but said he didn't remember a fly being on his food.
In rare cases, flies have laid eggs on fruits and vegetables that have recovered from stomach acid and hatch in the intestines.
Doctors wrote about the case, published in the American Journal of Gastroenterology: 'This case represents a very rare colonoscopy finding.
'[It's] a mystery as to how a fly found its way into the large intestine.'
Flies and their larvae can enter the human intestine in a condition medically called intestinal myiasis. This happens when a person consumes food containing fly eggs and larvae.
In rare cases, these can survive the acid in the stomach and then enter the intestines, grow and possibly turn into adult flies.
The Centers for Disease Control and Prevention (CDC) says some infected patients have no symptoms, but others have abdominal pain, vomiting and diarrhea.
It is unclear what food the man may have eaten that contained fly maggots, but this has previously been linked to rotten bananas.
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