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.