Keep. Your. Shoes. On.

This is the resolute advice of a flight attendant revealing the insider secrets of what goes on at 35,000 feet.

“Keep your shoes on. The floor is so filthy it’s ridiculous,” the anonymous cabin crew member wrote on a Reddit thread when asked what it is passengers don't know about air travel.

The question sparked a torrent of comments from past and present airline staff on the aspects of flying that are best kept quiet.

“There are sometimes body parts in the storage area near your luggage,” claimed one user. “When they are flying transplants for hospitals. Also your pets are in the same area.”

Another user, who claimed to be a member of the ground crew, added: “We send full bodies on planes a lot. Some in caskets, some not.”

A less macabre revelation came from another user, confirmed by a few others, that if you annoy the cabin crew, one of them is likely to break wind in your vicinity. “The farting thing is true,” apparently.

Keeping things crude, one former cabin crew member revealed that the staff know if two people slip off to the bathroom to join the Mile High Club, adding: "We can also open the doors, easily, from the outside."

There was also some practical advice issued by participants in the discussion, with the top rated comment urging passengers to “count the seat backs to the closest exit” as there was a “good chance you won’t be able to see in some… accidents”. This tip is sometimes given by cabin crew during the pre-flight safety briefing.

Another interesting piece of advice was that when told to place your hands in the “brace” position or cover your head with your hands, “do not ‘lock’ your fingers… but place one hand on top of the other”. The user continued: “If something falls on your hand/head, you’ll still have one good hand to use.”

When the cabin crew says to locate your nearest exit, do it Credit: © Alex Segre / Alamy Stock Photo/Alex Segre / Alamy Stock Photo

Also on the thread was the revelation of just how much pilots sleep during long-haul flights - a lot, it seems (don’t worry, there’s a co-pilot).

Another reiterated the recommendation of keeping your shoes on while walking up and down the aisle.

“Do not walk around barefoot. Pee and poop happens, all over. People get nosebleeds, or their wounds open. Obviously, when we land, it is thoroughly cleaned, but in-flight resources are limited,” the user wrote.

The same person commented on the cleanliness of the tray table - “unsanitary” - but this comes as little surprise, after a study in 2015 found it to be the dirtiest part of the plane.

Last but not least is the sad news that flight attendants do not like passengers repeatedly quoting lines from the 1980 aviation classic, Airplane!.

“[They] get really f****** old in the first week.”