Because great wyrms are so old, each one has at least one especially vulnerable spot upon its body. The dragon’s scaly hide will have been damaged by disease, combat, or by general wear and tear at these points, and nervous ganglia tend to gather there. During physical combat, a person striking at a great wyrm with a sharp-edged weapon (including arrows and hurled hand axes and daggers) has a 1% chance of accidentally hitting such a vulnerable spot. The blow will strike the dragon as if against AC 4, and the blow will do double damage to the wyrm. The wyrm will immediately retreat if struck in such a spot, and will attempt to find safety and recover from the wound. Magical attacks, even magic missiles, will not affect the wyrm in this way. If a vulnerable spot is located and recognized, attackers may strike at the spot further unless the wyrm covers the spot or moves it out of reach of weapons.