Stick a sane person in a padded room for long enough and he or she will eventually go a little mad.
The same appears to hold for air travel.
Put someone on a plane and the strange sensation of flying through the sky seems to make us behave oddly -- suddenly the normal rules of acceptable behavior are sucked down the pan, along with all that startling blue liquid.
Witness the recent event in the United States when a pilot had a breakdown mid-flight.
But it's not just crew that can be affected -- passengers crammed into a claustrophobic metal tube with two or three hundred others are also vulnerable to odd deeds.
"Some people are clautrophobic, so remaining in tight quarters for hours would ramp up their anxiety," says Richard Cytowic, a neuropsychologist and author of various books on neurological conditions.
"They might become suspicious -- for no objective reason -- that something could go wrong with the plane, and then this stream of thinking could escalate to a full-blown panic attack.
"Other people don't like to sit. I have a friend, a well-known landscape architect, who doesn't have any chairs in his home! 'I have to move around,' he says, 'And I work standing up at an antique architect's desk.'"
So what strange things do passengers get up to at 30,000 feet? With a little light analysis from Dr Cytowic, here are some of my observations.
Drinking tomato juice
The singular most unfathomable antic of normally tasteful people on planes is our overpowering need to drink tomatoes.
We don’t drink this stuff, ever, during normal life. What makes it irresistible now?
This is a salad product that tastes OK at best, even when secreted within more delicious peers such as avocado and beetroot.
I will concede I have also fallen victim to the "tomato juice conspiracy." However, mine has always come with vodka, Tabasco, Worcestershire sauce and a stick of celery (see below).
Dr Cytowic says: "The fact that it is offered when we don't go to the effort of keeping it at home makes it seem desirable -- and so we say, 'I'll have a tomato juice.'"
Doing squats and ankle flexes in public
We don’t want to get deep vein thrombosis, we need to exercise, we must stretch our legs.
I’m not saying we shouldn’t do it, I’m just saying it looks weird.
And if we have to, can we do it without thrusting our smelly feet and sweaty behind into someone else's face?
Dr Cytowic says: "We've read such advice in papers and magazines. They warn about deep vein thrombosis -- which is no joke and often is lethal. So we engage in aisle yoga, or in-seat isometrics."
Drinking at 10 a.m.
Some people claim the only way to get through a 12-hour flight in economy class without becoming a child murderer is to crack into the booze as soon as possible.
Damn right. And if breakfast's only just been cleared, so be it.
Screaming kids, faulty entertainment systems and fat guys sleep-dribbling onto your shoulder -- not exactly joyous things to experience anywhere, but when sharing two cubic meters with all three, you've got to do something to keep the rage from rising.
Alcohol fills that role quite soothingly, so thank God for miniatures and Champagne welcomers.
Dr Cytowic says: "For leisure travelers, they might be in a 'it's the start of vacation' mood, and so a drink sounds like a treat. People often drink at Sunday brunches, so the sense of it being an 'off day' may give them license to indulge."
Reading bad books
There are two points to make here. Plane travel has a bizarre effect of making non-readers suddenly want to look bookish.
A bit like those salad-dodgers who decide a small glass of tomato juice would go down nicely right about now (see above).
So that’s good.
But it also makes real readers, who enjoy spending a few hours each weekend with Hemingway, Dickens or Joyce, suddenly reach for “My Mother was a Washing Machine” or “Me.”
Look that last one up. It’s real. Ricky Martin. ‘Nuff said.
Dr Cytowic says: "This I know nothing about. I suggest that passengers read my books! They are good entertainment, I promise."
Going to the toilet for a change of scenery
Most of the time washroom protocol is get in, get rid, get out.
Yet there is something about a plane’s claustrophobic WCs and their excess of toiletry goods and cubbyholes that makes them appealing as places to simply, hang out, occasionally.
Perhaps it’s the privacy. Perhaps it's to escape those life-sapping kids and aisle-yoga practitioners.
Or perhaps it’s just me.
Dr Cytowic says: "On-board nervousness, I'd guess. But then no one knows what's going on in the minds of passengers in the cabin toilet. These secrets will endure."
Your turn. Noticed any other things people only do on a plane? Tell us about them below.