Rodents like rats, mice and squirrels are the most numerous mammals on the planet. This programme reveals how, with their constantly growing, chisel-sharp front teeth, they are specialists in breaking intoseeds. It also shows how they have adapted this talent to help them make their homes and even live underground, as well as revealing their ability to store food - and their ability to breed prolifically.In Panama, David Attenborough fails to smash open a tropical nut with a large rock. Yet the terrier-sized agouti can easily gnaw through the concrete-hard casing to get at the nutritious kernel inside.Like several rodents, the desert kangaroo rat stuffs seeds into its cheek pouches to take back to its burrow for safer eating, while the strange-looking naked molerat lives its entire life underground, using its massive incisors for digging tunnels and ripping apart buried tubers for food. Beavers can even cut down trees with their front teeth, using the logs for building their dams and lodges. A tiny infrared camera inserted into a beaver's lodge shows how they stay active during winter, feeding on the leaves and branches they stored under the ice in autumn. But unknown visitors also reveal themselves on camera - a family of muskrats sharing the lodge, tolerated perhaps in exchange for a regular supply of fresh bedding for the beavers.Rodents are known for being prolific breeders. In Australia, this can cause such plagues that farmlands and homes are literally overrun by carpets of running mice. The largest rodent in the world, the capybara, also occurs in huge numbers, but they live in the vast swampy grasslands of South America so there is plenty of room to graze in great herds.