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"Nova' episode gets its teeth into fascinating crocodile facts

Did you know a crocodile can float or sink at will, controlling its buoyancy like a submarine? And did you know that some have special glands in their mouths that enable them to tolerate saltwater long enough for the occasional seaside swim?

Neither did I. But now I know almost more than I need to know thanks to Crocodiles!, tonight's edition of PBS' Nova, hosted and narrated by David Attenborough. Does it make me like crocs any better? Not much, particularly after those shots of a croc sashaying down a beach that once looked pretty inviting, then splashing into the surf.

Let's say I respect the critters, but I can't really warm up to them _ even after Attenborough goes to such lengths to make us appreciate the problems they face raising baby crocs in a world filled with predators and precious little food. I respect them because they're survivors _ descendants of reptiles who have hung on for 17-million years virtually unchanged while their cousins, the dinosaurs, are nothing but fossils or special effects.

Here's another thing you probably didn't know: Crocodiles and their relatives, alligators and caymans, communicate by grunting. Nova tells us they can do at least 18 different grunts and that the American gator is the most vocal, while the crocodiles of the Nile river are quiet and subtle by comparison.

Tonight's show includes a number of remarkable sights. One is the calm, determined effort of some zebras to swim through a mess of crocodiles. Turns out a zebra can bust a croc's jaw with a well-timed kick, so it's not exactly Mike Tyson versus Buster Mathis Jr. every time a croc takes one on. You will, however, get to see the crocs at a zebra buffet.

Another peculiar sight is a pride of lions trying to defend a carcass against a hippo and a fearless croc. Seems that croc hide is tough chewing for a lion, and those big croc jaws look scary, even to the king of beasts. The lions finally decide a movable feast makes more sense than taking on the croc and all his fellow diners.

On the other hand, crocodiles don't play chicken with hippos, which can snap a croc in two with minimum effort. They often avoid that kind of trouble and wait for the other guys to finish. Since their digestive juices are super-acidic, crocs can be content with a meal of hide and bones. As Attenborough tells us, "There's no such thing as crocodile leftovers."