There was never anything to be gained from observing what humans said — Reaper Man

"Then there was a silence. It was the particularly wary silence of something making no noise. (p. 124)"

"He lay back and smiled. It was never too late to have a good life. (p. 311)"

"Windle shook his head sadly. Five exclamation marks, the sure sign of an insane mind. (p. 262)"

"Intellectually, Ridcully maintained his position for two reasons. One was that he never, ever, changed his mind about anything. The other was that it took him several minutes to understand any new idea put to him, and this is a very valuable trait in a leader, because anything anyone is still trying to explain to you after two minutes is probably important and anything they give up after a mere minute or so is almost certainly something they shouldnt have been bothering you with in the first place. (p. 38)"

"In a general sort of way everyone knew they were going to die, even the common people. No one knew where you were before you were born, but when you were born, it wasnt long before you found youd arrived with your return ticket already punched. (pp. 11-12)"

"It cant be intelligent, can it?" said the Bursar."