Tubercles, or bumps, on the leading edge of the flippers of humpback whales (Megapteranovaeangliae) increase the angle of attack at which such flippers lose lift dramatically or ‘stall’. This stall-delay is thought to enable greater agility. Brenner has carried out a mathematical analysis of the lifting properties of a wing with slowly varying cross section, and has demonstrated that the bumps alter the pressure distribution on the wing to delay separation of the boundary layer, leading to a gradual onset of stall and higher stall angle. His results agree quantitatively with experiments. The results suggest a new mechanism for increasing the maneuverability of flying vehicles.