Last one was:
Ok, so this one was a little tough, I think. If you change the Japanese a little, you have: 無い「す」なスイカは、何になでしょう？This riddle doesn't work in English, but in Japanese, 「すいか」is "watermelon." Figuring out what the question is asking is the main park of this one! It wants to know, "「すいか」without the 「す」becomes...what?" And in Japanese, 「いか」 is squid. So a watermelon without it's 「す」becomes a squid.