Cats cannot smile. They do experience emotions, including happiness. Cats have several physical ways of expressing pleasure, such as high-pitched meowing, a vertically position to the tail, narrowed pupils and a low, trilling purr.
Perhaps one of the most famous smiling cats in Western literature is the Cheshire Cat from "Alice's Adventures in Wonderland" by Lewis Carroll. The cat appears and disappears at various points in the story, vexing the young heroine with humorous philosophical comments. It is thought that the character was inspired by a Cheshire cheese molded to look like a smiling cat. It is also the origin of the phrase "grinning like a Cheshire cat."