mass-produce explosive material, like gunpowder. However, they are fairly advanced in other areas, such as the field of medicine. Regalian culture revolves around defending their "light," both literally and figuratively, as they use the word "light" as an idiom for "life.” Underland humans and their bonds are always prepared for a fight, and rarely host cultural events unrelated to their continued survival. Bonding Underland humans developed the tradition known as "bonding" shortly after their arrival in the Underland, and have put it into constant use since then (primarily with fliers). When two creatures bond, they are bound together forever through a formal promise to defend the other. In the dangerous environment of the Underland, this is a coveted and extremely serious relationship. The punishment for forsaking a bondmate — referred to as one's "bond" — is banishment alone in the Dead Lands, which means almost certain death. Very rarely, one can be bonded to more than one creature — in Luxa's case, she was able to bond to both Ripred the gnawer and Aurora the flier. Each of a pair of bonding creatures must recite an oath in front of an official gathering, which is often followed by a celebration. The oath goes as follows: (Bondmate's name) the (species name), I bond to you. Our life and death are one, we two. In dark, in flame, in war, in strife I save you as I save my life. Tree of Transmission The "Tree of Transmission" is a visual representation of the Underland equivalent of Morse code, i.e. a method of transmitting information over long distances using repeating patterns. The code has no official name, as it is the only code to have been created by humans, rats, mice, spiders, crawlers, and bats together. It is very similar to Morse code, but with a few important differences. The first is that it is only transmitted with sound, usually through the stone of tunnels, while Morse code can also be used by switching a source of light or electricity on and off. This is because of the code's use of three distinct sounds (a "click,” a "scratch," and a "tap"), while Morse code differentiates symbols only through the length of transmission. The other main difference from the Overland code is the lack of number symbols. The Tree of Transmission is so named because of one of the humans' ways of representing it.