Suppose a man was struck by an arrow thickly smeared with poison. Their friends and colleagues, relatives and kin would get a surgeon to treat them. The surgeon would cut open the wound with a scalpel, probe for the arrow, extract it, and expel the poison, leaving some residue behind. Imagining that no residue remained, the surgeon would say: ‘My man, the dart has been extracted and the poison expelled without residue. It is still capable of harming you. Eat only suitable food. Don’t eat unsuitable food, or else the wound may get infected. Regularly wash the wound and anoint the opening, or else it’ll get covered with pus and blood. Don’t walk too much in the wind and sun, or else dust and dirt will infect the wound. Take care of the wound, my man, heal it.’

They’d think: ‘The dart has been extracted and the poison expelled with no residue. It’s not capable of harming me.’ They’d eat unsuitable food, and the wound would get infected. And they wouldn’t regularly wash and anoint the opening, so it would get covered in pus and blood. And they’d walk too much in the wind and sun, so dust and dirt infected the wound. And they wouldn’t take care of the wound or heal it. Then both because they did what was unsuitable, and because of the residue of unclean poison, the wound would expand, resulting in death or deadly pain.