Rough music
Despite indulging in a good deal of nosiness and gossip, rural folk far from the purview of policemen and magistrates tend toward minding their own business and living and letting live. This is until the lack of policemen and magistrates encourages someone to exceed the reasonable bounds of social behavior and make himself such a danger or annoyance to his neighbours or such an affront to their sense of decency that there is a sudden shift of opinion toward retribution. It is then that the offender needs policemen and magistrates, for the outraged mob is seldom as merciful as the Laws that rule more populous areas. This lynch-law or vigilantism may be a crude but effective justice or a tragic injustice; it is not governed by reason and the mob mentality is seldom interested in proof or a fair trial.
On the Chalk this crescendo of aggrieved self-righteousness is called the rough music, the dissonant piping and war-drums of vengeance. It plays when Seth Petty nearly beats his daughter to death and causes the abortion of her baby. Despite some doubt, Tiffany Aching manages to prevent another killing when a mob nearly as drunk as Petty comes after him.
Rough Music is a tune anyone can dance to. Even Sam Vimes has swayed to its rhythm, once when Carrot restrained him from performing an informal execution on Doctor Cruces, and once when only Detritus stood between him and a child-killer who was discovered to have taken souvenirs from the murder scene.
Granny Weatherwax once managed to turn its volume down with her own anger, suggesting the appropriate punishment to a rural child-killer who begged for mercy claiming the crime had been done in drink. "In sobriety, end it in hemp." She got very angry at the complacent statement from a Lancre rough musician that "justice has been done".
Among the desert tribes of Klatch there is an absolute requirement of hospitality. The ancient rule requires anyone to provide shelter, food, drink and safe conduct to anyone who appears out of the very inhospitable desert, though it be his most ancient and despised enemy, for a period of three days. It is unthinkable and nearly impossible that one of their culture should forsake this obligation, but... There is among them a policeman of sorts, a desert ranger, who is also a trained and licensed Assassin with another layer of etiquette and tradition. Once, a man who poisoned a well came by chance to the camp of Ahmed the policeman. A whole village had died (and several valuable camels) and despite the restraints of his dual cultures Ahmed acquired the prefix "71-hour" when the rough Klatchian music played because sometimes the rules just don't cover the situation.
Roundworld parallels might include the public hysteria over paedophiles - this resulted in a slightly dyslexic mob who could not quite read the score for the rough music going to the home of a self-declared paediatrician and burning her house down. The "satanic abuse" hysteria that swept the USA and even washed over parts of Britain, such as Rochdale and the Shetland Islands, is an equally valid example.