How did Scrooge try to explain its presence? (the ghost)

Scrooge tries to explain Marley's presence as a case of indigestion.

"Because," said Scrooge, "a little thing affects them. A slight disorder of the stomach makes them cheats. You may be an undigested bit of beef, a blot of mustard, a crumb of cheese, a fragment of an underdone potato. There's more of gravy than of grave about you, whatever you are!"