"Channeling capacity is pretty well understood practically speaking. Wizards know how to use it, how to tell how much of it someone has, we even have a half an idea of why some people have more of it than others, we can increase our supply by getting familiars - and nobody knows what it is. Firebirds are a... bird. That does fire. They live near the sun. Wolfriders are two parallel species, wolves and riders, who have natural mindlinks with their opposite numbers starting when they're a couple days old."