Christmas morning when my five-year-old opened up the fish tank we gave her the reaction from her older sister was...well, jealous. "How come she got a fish?" were her exact words. "She asked for one," I responded. Then I quoted: "which of you fathers, if his son asks for a fish, will give him a snake instead". The response? "Can I have a snake?". For real! And she won't give it up now. I'm thinking of answering this way the next time she brings it up: "Which of you mothers, if her daughter asks for a snake, won't give her a fish instead?".
Incidentally, the fish came into our house because my daughter had tired of begging for a dog and (smartly) switched tactics and angled for a fish. I'm not ready for a dog. But a fish? Well, I guess that's still to be determined, huh?