Whistle To Warn Him

Jones was sitting with his wife behind a palm on a hotel veranda late one night when a young man and girl came and sat down on a bench near them. Hidden behind the palm, Mrs. Jones whispered to her husband, “Oh, John, he doesn’t know we’re here and he’s going to propose to her. Whistle to warn him.”
“What for?” said Jones, “Nobody whistled to warn me.”