Why does my mouse fill his water dish with shavings?

God of Answers, Knower of All Things:

I have owned several pet mice over the years, and year after year, mouse after mouse, they all engage in one behavior besides the usual poop-eat-sleep cycle. When I fill any given mouse's water dish, the first thing he will do is rush over to the water and throw in some of the wood shavings that line the bottom of his cage. Is my mouse neurotic? Is it a natural instinct gone bad?

-- A Really Bored San Diegan

Behavioral analysis of the short end of the food chain, a link or two north of barnacles and squash, is pretty darn unrewarding. After much burrowing and digging, most of it through the American Fancy Rat and Mouse Society, we came up covered with wood chips and barely smarter than when we started. Mousekeepers are not an inquisitive lot, so answers are few. Simple pets for simple minds? Who knows. We did finally corner a mouse expert, apparently not a fast runner, who agreed to put her rep on the line. Any caged mouse, not just yours, will fill its water bowl with whatever crud is on the floor. This may be because rodents are not fond of bodies of water. Mice in their natural habitat wouldn't have water lying around the house. And, second, mice while away their limited hours on earth organizing the things around them, shoving cage shavings back and forth and rearranging the furniture. So your pet finally gets the cage feng shuied, when in comes this big hand that whips out the nicely hidden dish, then sticks it back in with more of that danged water. Well, what's a mouse to do except start all over again burying the dish from hell? Big bulletin to you from the society of folks who raise fancy rats and mice: Don't give mice water in bowls. Part with a fiver and get one of those gravity water bottles. Your pet will thank you; your problem will be solved.