What compels hundreds of otherwise law-abiding people to descend on a beach and make off with a stash of seemingly useless plunder?
Steering wheels, seatbelt components, air bags, foreign language bibles - these are just some of the goods to have been carted off from Branscombe beach in Devon by scavengers.
While the morals of slipping away with a brand new BMW motorbike or a cask of wine are questionable, the logic is at least clear.
The same can't be said for the car exhaust fittings and gearbox units that were carried away from the beach close to where the container ship MSC Napoli had run aground off the south coast of England.
How many pairs of shoes or tubs of beauty cream can anyone really need? Coastguard officials accused scavengers of "sheer greed".
Yet still they came, and many couldn't even explain their motives.
"There's plenty... there's a container down there - the more we can take away the better really - it's not really any good to anybody is it?" said one "have-a-go" salvager.
"We've been trying to get a BMW bike but we ended up with BMW parts instead... and cat food. But I don't even have a cat," said another.
Many said they would try to sell their haul on eBay, and last night a number of airbags retrieved from the beach had appeared on the website.
But it's a fair bet that much of what was taken will languish in garages and lock-ups for a few weeks before being thrown away.
The Sun newspaper labelled it the "January sails" and consumer psychologist Paul Buckley says the pun is a fitting one.
"Consumers aren't very rational, whatever the research might say. People don't think out what they do. They make quite emotional decisions on products," says Mr Buckley.
"Watching those guys down on the beach on the news at 10 o'clock last night, it was like seeing people on the High Street at sale time. There is the thrill of the chase for a bargain, and the social aspect we have in getting something for almost nothing... or nothing in this case.
"We like to tell others about it."
With police looking on, many felt entitled to scavenge
Mr Buckley senses a sort of "survival instinct" at work among the scavengers.
"It's a bit like watching aid convoys distributing food in war-torn countries. If others are clambering for something and there's a scarcity, we don't really question whether we actually need whatever it is."
While some of the plunderers will surely have woken up on Tuesday morning wandering just what compelled them to grab a stash of gearboxes, there is also an ethical question to be considered.
Salvaging for personal gain is illegal, yet many of those who found their way to Branscombe beach on Monday wouldn't consider themselves criminals.
So how do they justify it? Some have pointed to the long history of wreck plundering off the south-west coast, implying that it's in the blood of locals. But the laws are not new - they were around in the late 18th Century, although were widely ignored then too.
"People are clearly able to draw a dividing line and say this is a victimless crime even though they vaguely appreciate it's against the law," says social psychologist Ian Vine.
"The one thing that people are really good at is excuse-making when they do things they know they shouldn't do."
Morality, he says, tends to operate on a one-to-one basis - one person behaving morally towards another.
"When it gets to extending these principles of fairness and consideration not to a person, or a group of people, but a faceless shipping operator, our intuitions get subverted. We don't think we're doing anything wrong."
The novelty of the situation will have helped people sidestep their normal principles, he says.
"In most situations we know what the moral code is, and the role that's expected of us. But in situations where there's not a clear role or several possible roles then we turn elsewhere for guidance on what we should do - we look to see what others are doing."
The fact police - taken to be moral enforcers in such alien situations - were turning a blind eye to the scavenging further exacerbated people's uncertainty, fuelling the herd instinct.
"When you see other ordinary people doing something that you would hesitate to do, it tends to redefine your perception. It's a neat psychological trick."