I think that sick people in Ankh-Morpork generally go to a vet. It's generally a better bet. There's more pressure on a vet to get it right. People say "it was god's will" when granny dies, but they get angry when they lose a cow.
It takes a special kind of person to fight back.
It's not lying when you do it to officers!
It doesn't stop being magic just because you know how it works.
The brain works fast when it thinks it’s about to be cut in half.
Racism was not a problem on the Discworld, because - what with trolls and dwarfs and so on - speciesism was more interesting. Black and white lived in perfect harmony and ganged up on green.