[Har-har-har!]

The clue in this crossword puzzle is “[Har-har-har!] is KNEESLAP.” The answer that fits in the blank spaces is Kneeslap. The phrase “Har-har-har!” is often used to indicate laughter, and a “Kneeslap” is a common physical reaction to something funny. It involves slapping one’s knees together as a reflexive response to humor or amusement. Therefore, the answer to the crossword question is kneeslap because it is a physical action that often follows laughter.