Full Idea
If the cat appears at one moment in one part of the room, and at another in another part, it is natural to suppose that it has moved from the one to the other, passing over a series of intermediate positions.
Gist of Idea
If the cat reappears in a new position, presumably it has passed through the intermediate positions
Source
Bertrand Russell (Problems of Philosophy [1912], Ch. 2)
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.10
A Reaction
This example seems perfect as an illustration of inference to the best explanation (now called 'abduction'), and that seems to me the absolute key to human knowledge. The cat example is what made me a devotee of Bertrand Russell.