David Attenborough turns his attention to the sloth, an animal whose entire biology runs on a diet of leaves too poor in nutrition to support much activity. The footage shows how that constraint shapes everything: a slow metabolism, a specialized gut built to extract every possible calorie, and movement so deliberate it doubles as camouflage from predators watching the canopy. Attenborough narrates the sloth's life among the branches, then the segment breaks its own premise by catching one moving at surprising speed, a reminder that the lethargic stereotype only tells part of the story. The clip also notes the sloth's role in its ecosystem: as it travels between trees it disperses seeds, helping regenerate the forest it lives in. It is a short, focused case study from the BBC's Life of Mammals series, built around a single question, how does an animal survive on almost no energy, and answered entirely through what the camera catches in the treetops.