Whistle!

Old man Murphy and his wife went for a stroll in the park. They sat down on a bench to rest for awhile, and soon began to overhear voices coming from a secluded spot nearby.

Suddenly, Mrs. Murphy realized that the young man they were hearing was about to propose! Not wanting to be eavesdropping during such an intimate moment, she gently nudged her husband and whispered, "Whistle to let that young couple know that someone can hear them."

"Whistle?" Murphy replied. "Why should I whistle? Nobody whistled to warn me!"