Sometimes, if they decide that the question is interesting or easy, they'll even answer it themselves. Once a guy wrote in because his five-year-old daughter wanted to know if there was any animal starting with the letter "X".
X-ray fish. :)
(Note: I'm recommending this for serious writers, mainly. They're required to take everyone seriously, but if you write in for a fanfic or RP information, that's a pretty gross waste of gov't time. I remember someone who wrote in to ask how much a fairy would weigh on Planet Imaginary if her bones weighed such an amount and her hair fell down to her butt. Don't be that person!)