Magic is present in all people to a degree. This magic creates what can be loosely described as a field that is characteristic of that person (particularly if that person has strong aura) and has a tendency to "rub" on things that persons owns. This is especially true with magical tools. This field is properly called an Aura, but the slang term Dose may also used among wizards.
Auras can vary in their intensity and the more intense the aura, the more likely the person will have magical abilities and wizwitch tendencies. Magic users have a greater aura and Zarkians, Sneeches and Fratzers in particular have a very intense auras. However there are other characteristics of an Aura and some people may have a good deal of it but still never become magic users.
Causes and influences
What causes auras in people and why some people have it bigger than others is not known precisely in the Mansionland. Genetics are an uncertain factor: it is possible to have two parents that have an intense aura and they be wizwitches and give birth to a child that has almost none. That said, certain families (namely the Silverjohns, the Dresdens and Cravens and probably a few more) do tend to reliably produce wizwitches.
There is evidence that being born at a Tricklepoint and growing up on them can make an Aura stronger.