Brain fats cleared during sleep, and bird poo powered Peru

Today, how the brain harnesses immune cells to clear burned out fats during sleep: does this protect from Alzheimer's disease? Also, the nutrient-rich guano of seabirds that shaped society in ancient Peru, fast footage reveals how kangaroos hop faster at no extra energy cost, and how horses whinny! Like this podcast? Please help us by supporting the Naked Scientists (thenakedscientists.com/donate)