The peregrine falcon reaches faster speeds than any other animal on the planet when performing the stoop, which involves soaring to a great height and then diving steeply at speeds of over , hitting one wing of its prey so as not to harm itself on impact. The air pressure from such a dive could possibly damage a bird's lungs, but small bony tubercles on a falcon's nostrils are theorized to guide the powerful airflow away from the nostrils, enabling the bird to breathe more easily while diving by reducing the change in air pressure. To protect their eyes, the falcons use their nictitating membranes (third eyelids) to spread tears and clear debris from their eyes while maintaining vision. Peregrine falcons have a flicker fusion frequency of 129 Hz (cycles per second), very fast for a bird of its size, and much faster than mammals. A study testing the flight physics of an "ideal falcon" found a theoretical speed limit at for low-altitude flight and for high-altitude flight. In 2005, Ken Franklin recorded a falcon stooping at a top speed of .