I don't think there are any laws against concrete floors. I don't remember too well, but I'm pretty sure at the Houston Zoo the elephants, giraffes, bears and half the big cats live on some variation on a concrete floor. And the bears at the Houston Zoo live in surprisingly tiny enclosures. Not only are they tiny, but they're extremely narrow. The enclosure itself is pretty large, but most of it is taken up with a giant moat to protect visitors that takes up about 80 percent of the exhibit. The bears actually live on a tiny strip of rock or concrete behind the moat.

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"You gotta help us, Doc. We've tried nothin' and we're all out of ideas!"