Using jokes is a great way to introduce students to how humor and abstract thought are connected.  Virtually all kids are familiar with the simple humor found in basic jokes that require minimum effort to comprehend.  I use a variety of jokes, from the concrete to the abstract, to help students begin to understand that some of the things we find the most humorous involve the most thought.  As with all of the activites provided, student-to-student interaction is imperative.  Discussing their interpretations of these jokes with their peers, and sharing new jokes with each other establishes the relaxed climate that encourages the abstract thought that we hope to foster.

Joke archive from Reader's Digest: http://www.rd.comjokes/

Here is a sample of some of the jokes that I've gathered over the years and use in class. These progress from fairly concrete to requiring prerequisite knowledge of math, history, or vocabulary: Jokes.doc (30,5 kB) 

Joke and Riddle Matching Activity: Joke Riddle Matching.doc (23,5 kB)

*One of our favorite assignments is to ask students to bring in a joke (clean, of course) to share with the class.  The only requirement is that their joke must be something they think will stump their peers and they will need to explain.