very large dogs or small ponies, and reach their full size after eighteen months. Because young dragons grow so fast, their riders must regularly apply oil to their hides to prevent the skin from cracking or drying out. Dragons, like their fire-lizard ancestors, can breathe fire by chewing a phosphine-bearing rock, called "firestone" in the novels, which reacts with an acid in a special "second stomach" organ. This forms a volatile gas that can be exhaled at will and ignites upon contact with air. The flame is used to burn Thread from the sky before it reaches the ground. However, the chewed firestone must be expelled from the body after it is used up, for the dragons cannot digest it. Psychic abilities Despite their relatively low intelligence, fire-lizards communicate through a form of weak telepathy. They also imprint on the first individual who feeds them after they hatch, creating a telepathic bond with them; the Pernese call this phenomenon "Impression". In creating dragons, Kitti Ping intensified the creatures' telepathy, greatly increased their intelligence, and gave them a strong instinctive drive to Impress to a human. Upon hatching, each dragonet chooses one of the humans present (usually) and Impresses to that person; from that moment on, the pair are in a constant state of telepathic contact for as long as they both live. Dragons also use telepathy to communicate with each other and with fire-lizards. They are capable of speaking telepathically to humans besides their own riders, but not all of them will do so except under unusual circumstances. Dragons and fire-lizards can also teleport. They do this by briefly entering a hyperspace dimension known as between. Both humans and dragons experience between as an extremely cold, sensory-deprived, black void. After spending no more than eight seconds in between, the dragon or fire-lizard can re-emerge anywhere on Pern, along with any passengers or cargo they carried. This ability is explained as having evolved in fire-lizards as a defense against Thread; not only does it allow them to quickly escape from Threadfall, but the intense cold of between kills any Thread that has already burrowed into them. If a dragon attempts to teleport without a clear mental image of the place where they intend to reappear, they may simply fail to emerge from between and thus, be gone forever. Going between allows dragons to travel through time as well as space, as