- "If you're going to suggest I try dropping twenty feet down a pitch dark 
  tower in the hope of hitting a couple of greasy little steps which might 
  not even still be there, you can forget it," said Rincewind sharply. 
- "There is an alternative, then." 
- "Out with it, man." 
- "You could drop five hundred feet down a pitch black tower and hit stones 
  which certainly are there," said Twoflower. 
Dead silence from below him. Then Rincewind said, accusingly, "That 
was sarcasm." 
        -- (Terry Pratchett, The Light Fantastic)