Comedian Joan Rivers was known for her fearless, acerbic wit, but she could rein it in when the occasion demanded — like in July 1983, when she was guest-hosting The Tonight Show and the guest was Fred Rogers. "For me, it's like talking to a teacher," she told Mr. Rogers. "I can't say, you know, 'Have you ever fooled around?'" Rogers was promoting a book, and he disarmed Rivers as much as she needled him. The interview is interesting as a showcase of Rivers' softer side, but you also learn a lot about Mr. Rogers. Like, his mother knitted every one of his famous sweaters, giving them out every Christmas. (Rivers: "That's wonderful, in a way — and in a way it's very boring, because you knew what you were getting.") Tip-toeing up to the line, but never quite crossing it. --Peter Weber