Whomping Willow

This is the first chapter in the Harry Potter series named after a magical plant. The Whomping Willow is an ancient, very valuable, and very vicious tree planted in the Hogwarts grounds. Harry and Ron Weasley first encountered the Whomping Willow when Ron smashed his father's flying Ford Anglia into the tree, which then started to "hit," "smash," "attack," "pummel," "punch," "pound," "lash out," "pound," and "wallop" the two boys and the car with a "hail of blows from knuckle-like twigs" and "vicious uppercuts" from "branches as thick as a battering ram." Ouch. (CS5).The next year Harry's Nimbus 2000 broomstick was blown into the tree and was smashed to bits (PA9).

This tree was planted the same year that Remus Lupin arrived at Hogwarts to conceal an opening to a secret passage from the Hogwarts grounds to the Shrieking Shack. Just before the full moon, Lupin would go to the Whomping Willow, use a long branch to press a knot in the trunk of the Whomping Willow (which temporarily immobilized the tree), and descend down a tunnel to the Shrieking Shack, where he could turn into a werewolf and not hurt anyone else (PA10, 17, 18, 19, 21).

Only the four Marauders knew how to enter the secret passage. Interestingly, although the Marauder's Map shows the secret tunnel leading from the Whomping Willow, it does not tell the reader how to enter it - although the map did reveal how to enter the secret entrance through the humpbacked, one-eyed witch.