This piece contains language which some might find offensive
In parts of the world blessed with effective, modern sanitation, it's widely understood that poo belongs inside a person, or a toilet.
But if you follow the news, you might have noticed an abundance of stories about "serial poopers": people who brazenly defecate in public, leaving shock (and, well, turds) in their wake.
The latest case involves a businessman from Brisbane, Australia, who has been charged with creating a public nuisance after reportedly fouling the same private path up to 30 times.
Are tales like these down to unfortunate medical conditions? Or is public pooing an extreme act of rebellion?
We asked a psychologist and an anger management expert what drives people to drop their pants in public...
'Soft or hard?'
Professor Mike Berry, a clinical forensic psychologist at Birmingham City University, says rage, anxiety, a desire to send a message, alcohol or illness could all be responsible.
"It's interesting," he says. "I've worked on cases where burglars have crapped in the house - and I always ask the police whether it's soft or hard. They look at me like I'm absolutely mad. And I say, if it's soft, then it's somebody who's anxious, so you get a kid who goes and craps on the bed. And if it's really hard stool then it's an indication of somebody who's angry and bitter about what he's doing."
Another key question is: Does the culprit do it repeatedly in the same place? If they're regular (so to speak), "it becomes a message to somebody or some people," says Prof Berry.
Obviously, there are unfortunate situations in which someone with an upset stomach or a more serious bowel condition might be unable to make it to the toilet in time. But looking purely at those who do it deliberately, we can divide the cases into one-off incidents, and systematic campaigns.
A furious Canadian woman arrested last month appears to fall into the first category. She was caught on camera defecating on the floor of a Tim Hortons coffee house in British Columbia, then flinging the result at staff. It was later reported that they had refused to let her use the toilet.
In the second category - that of repeat offenders - we find examples like the Colorado jogger dubbed "the mad pooper", who sparked a police hunt last year after defecating outside a family's home for weeks on end.
'Fascination with faeces'
While the experts won't comment on individual cases, they agree that "serial poopers" are often trying to stick two fingers up to the world.
"Usually it's a statement like, 'Life is shit, so stand in it,'" says Mike Fisher, director of the British Association of Anger Management.
"I mean, somebody who defecates in public has mental health issues. It's as simple as that. If you're socialised, that's the last thing that you would do."
Mr Fisher notes that people who defecate in public may have scatological tendencies - or "a fascination with their own poo".
"I remember being on a workshop many years ago when a French bloke told us how when he was a kid, he would actually shit in the bath and smear faeces all over himself," he says. "That is a classic example of scatology."
And as an adult? "He's not smearing [it] all over himself, but he's still got the same fascination with his own faeces."
The American Council on Science and Health says public pooing could also point to an elimination disorder - a kind of condition where urine or faeces are passed in places other than the toilet. The behaviour may or may not be within the individual's control.
Every so often, a misplaced turd might just be the work of "someone who's halfway home from the pub," says Prof Berry.
"The guy gets caught short, and he's learned he can go and crap on the lawn outside number 3 because there's nobody there, but he can't go and crap outside number 33 because it sets off an alarm system with lights flashing, etc!"
Ultimate primal weapon
Misbehaviour with faeces violates one of society's last taboos.
If you doubt that, just look at the way poo is deployed in prison protests, where it functions as a primal weapon. No matter how powerless you might otherwise be, excrement is available (and disgusting) to almost all of us.
"We have the famous cases in the 70s where IRA men used to wipe the walls with their faeces as a protest," notes Prof Berry.
When it comes to stopping public defecators, the experts warn there's no single solution - and shaming them is definitely not the answer.
Mr Fisher says anti-social behaviour can be linked to trauma, which frequently stems from childhood.
"I would say most cases [of chronic anger] that I deal with are directly linked to unfinished business from the past," he says. "Not only unresolved anger issues - it might be rage issues, it might be shame issues."
How might that happen? He cites the example of a child who defecates in the family home and is severely beaten by one of their parents.
"Trauma is going to be manifested in a whole range of cognitive dissonances, or physical acting-out."
Maybe that's worth bearing in mind the next time a "phantom pooper", "faecal fiend" or "bowel movement bandit" hits the headlines.