It was the question that struck many Australians as they read about the bizarre case of Queensland's so-called 'poo jogger' this week: Why?
High-flying businessman Andrew Macintosh was publicly shamed after being caught on camera, crouching down and doing the deed with his own toilet paper in hand.
It is believed Macintosh might have ducked down a private footpath of an apartment block near his Greenslopes home about 30 times over the last year before being found out by angry residents.
But, disturbingly, the habit of defecating in public places is not as rare as you would hope, and it's not confined to Australia.
Last year, a female jogger dubbed the “mad pooper”, made world headlines for defecating on a Colorado family’s lawn for weeks during her morning jogs.
Months later, a copy cat "pooper" in the US city of Little Rock, Arkansas, dubbed the "s--- bandit" by irate locals began relieving himself in the driveways of residents’ homes.
So what causes people to behave in such a bewildering way?
Leading clinical psychologist, Grant Brecht, says the act can have an adrenalin rush similar to the feeling of taking a "hit of heroin".
"They are seeking a thrill and they get addicted to the way it makes them feel ... equating it to taking a hit of heroin," he said.
"It can make them feel invincible ... it can also tie into the idea of delusions of grandeur."
Mr Brecht says there are a number of reasons behind public defecation, spanning from elimination disorder - a diagnosable mental condition marked by the inappropriate passage of faeces - to incontinence.
"The thing is nobody really knows why," Mr Brecht said.
"There are so many different reasons behind it that there could be a different reason for every person that undertakes that type of behaviour."
The first thing to establish is whether the behaviour is intentional.
"Sometimes it appears as a type of vindictive rage," he said.
"It's the ultimate expression of aggression aimed at something or someone the person feels anger or envy towards. They feel so enraged that they defecate on that person's doorstep. They're motivated by their anger and that's what behind their behaviour."
Mr Brecht, who has been a clinical psychologist for more than 30 years, says his own theory is that in some cases it can be a form of obsessive compulsive disorder.
"A person might be feeling really anxious, they could be under a lot of pressure at work and one day they defecate in a certain place for whatever reason," he said.
"Then they feel this compulsion to return there every day because if they don't, they fear something could go wrong in their lives. It's like's when a person continues to wash their hands, or they put their shoes under their bed every night, it's fuelled by anxiety or fear that something bad will happen if they don't."
Sydney clinical psychologist Pandelis Tsomis could not comment on Macintosh's case but, in general, said such repeated behaviour could be associated with obsessive compulsive order.
"The only thing I can think of is obsessive compulsive disorder, where people act out a behaviour that makes no sense but has a soothing or relieving effect," he said.
"There could be emotional tension."
He said the act of defecating could be associated with relief.
"It's that obsessive compulsive drive - if I do not poo there, something bad may happen. Literature about obsessive compulsive disorder shows people think, 'I have to open and close the fridge or my parents will die in a car crash'. Or, 'If I don't drink four glasses of water, I may get cancer'. There is some sort of drive, obsession, something to reduce anxiety," he said.
"With OCD type stuff, it's irrational stuff, where instead of A leads to B, A leads to W, and you've missed a whole sequence of events in between.
"But you would have to interrogate that person and ask them to be honest ... without that you may never know," he said.
It may be that the reason for such acts has more to do with the body than the mind.
Studies have shown gastrointestinal problems are common for endurance athletes, with 30 to 50 per cent experiencing some kind of gut issues, according to research published in Sports Medicine.
And among elite endurance athletes, particularly long distance runners, the prevalence of exercise-induced gastrointestinal symptoms was found to be up to 70 per cent.
"It affects gastrointestinal function," says Melbourne exercise physiologist Yujin Lim.
"When running your body preferences blood flow, moving it away from the gut into lower limbs and extremities. From there your GI function is compromised and for some people these things can happen.
"To the extent of needing to defecate on a jog regularly ... that's potentially questionable."
Long distance runners were more likely to encounter these symptoms, he said.
"With more intensity comes more demand and more of the body trying to preference running function over other functions in the body, especially if it goes to extreme lengths."
Melissa Cunningham reports breaking news for The Age.
Simone is a breaking news reporter for The Age. Most recently she covered breaking news for The Australian in Melbourne.