The Hound of the Baskervilles

Holmes said that the appearance of the footprints changes because Sir Charles began running.

“Mortimer said that the man had walked on tiptoe down that portion of the alley.”

“He only repeated what some fool had said at the inquest. Why should a man walk on tiptoe down the alley?”

“What then?”

“He was running, Watson—running desperately, running for his life, running until he burst his heart—and fell dead upon his face.”