1. An action associated with laughter.
2. Most resemble mathematical formulas: clever, perhaps, but hardly occasion for knee-slapping.
3. It's not just that he introduces his music and comments on it with a knee-slapping mock-tentative delivery that establishes him hands-down as the 21st-century Jack Benny.
4. Then, a full-out knee-slapping laugh came out of me, catapulting me back to a time before I knew about self control.