Democratic presidential candidate John Kerry can laugh about the controversy over his Vietnam service -- at least on Comedy Central. Kerry was a guest Tuesday night on "The Daily Show" on the cable network. Host Jon Stewart peppered Kerry with tongue-in-cheek questions about his service, saying that he understood Kerry was never in Vietnam. Kerry says that's what he's heard too and he's trying to find out what happened. Stewart also asked another hard-hitting question: "Is it true that every time I use ketchup, your wife gets a nickel?" The candidate's wife, Teresa Heinz Kerry, is heir to the Heinz food fortune. Kerry replied he wishes that it was true.