Plants usually protect the goodness inside their seeds with very hard outer cases - as David Attenborough testifies after he has tried and failed to crack open a tropical nut by bashing it with a rock. 'Believe it or not' he proclaims 'there are mammals here in Panama which can break into these nuts with their bare teeth! 'They are agoutis, terrier-sized rodents, which chisel through the rock hard shells with their remarkable front teeth, as if it was butter. The reward is a protein-rich kernel, and all rodents from the tiniest harvest mice to the mighty beaver, have these special, constantly growing inscisor teeth, with chisel sharp enamel on their front edges, in order to get at food of this kind. Many rodents, like squirrels, carry away excess nuts one by one to bury them for eating later on. But the seeds of plants in the Mojave desert are so tiny, that kangaroo rats use special cheek pouches, like shopping bags, to carry enough seeds back to their burrows .The Gambian pouched-rat has the largest pouches of all, so that when they're stuffed full of date palm nuts the rats can hardly squeeze through the entrance to their burrows! Some rodents use their special front teeth to chop off vegetation or chew bark instead.

Canoeing in Wyoming, David Attenborough watches beavers fell massive trees with their front teeth and then build dams to rival anything that humans can achieve. In the deep cold-water ponds that are created, the beavers store branches and leaves underwater, so that even when its iced over they have a store of fresh food to take to the safety of their lodge throughout the winter. Naked mole rats stay underground all their lives finding roots and tubers by tunnelling hundreds of metres from their breeding chambers. Rodents are renowned for being prolific breeders and sometimes, in Australia, mice cause such plagues that the farms and are literally overrun by carpets of running mice! The largest rodents in the world, capybara, also occur in huge numbers on the swampy grasslands of South America. grazing in great herds, they look remarkably reminiscent of the antelopes to be seen on the grassy plains of Africa, in the next programme.