There aren't many things you expect to see when you look out of a plane window at 4,000ft.
Clouds and blue sky are usually your lot. So you can imagine this passenger's confusion when he turned to his left and saw a 'pole' sticking out of the clouds.
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To make things even weirder, he claims he was flying over the sea at the time so there shouldn't have been anything there anyway.
The passenger posted photographs of the mysterious pole to Reddit, inviting other social media users to explain it - especially if they lived in the area.
Photos of the flight path taken inside the plane show he was on a flight from Malaga to Bristol, cruising at an altitude of 4,650ft just off the British coastline on December 5 at about 11.08am.
One user suggested: "Could be a contrail from something launched up - that's what it looks like to me.
"What it is I don't know - not a sea person. Maybe a flair or something from a ship down below - although I'd expect a more chaotic path from a flair.
"For all I know it could be a chip in the glass or a beacon from an oil rig to give planes some sense of where they are if the instruments fail."
When the passenger replied to say it was definitely a physical object, some suggested if he was on the right hand side of the plane, he would have a perfect view of the Mendip transmitting station mast.
There's just one issue: the mast is only 924ft tall and he was apparently thousands of feet above that.
A few people tried to explain this, too. One pointed out that he was looking down on it from his view from the plane.
Another said: "I suspect the flight monitor may show a slight delay on that (or rather, update every minute or two) and a passenger plane landing at Bristol would surely already be starting descent by then. So it's probably lower than 4600 ft."
The mast is the tallest structure in south west England and broadcasts digital television and radio.
It certainly looks as though it could be the culprit.