For humans to wipe their feet on, so they keep the floor inside the house clean for cats.

Photo by Sylvar

Down is an unfortunate direction cats must occasionally travel, just so they can go up again.

Photo by Ali Smiles :)

Dinghys and boats are a means devised by humans to help cats catch water fowl.

Photo by zenera.

Just another willing heat source.

Photo by catgoesmurp.

Decks are large sheltered expanses of wood that humans often lay outside their houses for the use of cats.
Photo by srboisvert

Too big to eat. Too small to sleep on. Useless.
Photo by Per Ola Wiberg (Powi)

A very silly looking dog.
Photo by mickeymox