An estimated 25 million mice are used (and by "used", I mean "killed") in the course of scientific research every year. I don't really mind. Experiments on mice are vital to medical science in its ongoing quest to alleviate human suffering — a thing of which, being a human myself, I would like to see a whole lot less. Sorry, mice.
And all but the most grotesque scientific experiments have to be nicer than a mouse's usual fate. Wild mice don't die of old age. They're the Pringles in earth's food chain. As a super fast method of converting sunlight into meat, rodents are what Nature whips up a batch of when carnivores get the munchies.
As inconsequential as they are, then, it's always a shock to observe what clean, pleasant, surprisingly complex and independent little animals mice can be. They build things, groom each other, nurture their young, play, have distinct individual habits and preferences, seldom bite the Big Hand unless they're very frightened or in pain (and then a nip to warn, not injure), and are generally nicer, smarter and more complicated than a 99˘ puff of fur has any obvious reason to be.
The strains of mice used in laboratories are bred to such genetic homogeneity that they are said to be, for all practical purposes, clones. I wonder.