“You don’t believe in me”, observed the ghost.
“I don’t”, said Scrooge.
“Why do you doubt your senses?”“
Because”, said Scrooge, “a little thing affects them. A slight disorder of the stomach makes them cheat. You may be an undigested bit of beef, a blot of mustard, a crumb of cheese, a fragment of underdone potato…”
From ‘A Christmas Carol’ by Charles Dickens.