Any living being produces spirit, and holds a certain level within its body. Provided the being is healthy, it will also produce a slight surplus that eludes into the surroundings. This free spirit can form temporary "pools", but eventually fades.
As a rule of the thumb, animals generate spirit faster than plants, and the more intelligent/mentally active an animal is, the more they generate. The surplus also peaks with strong emotions of any kind.
Eodean and other magic system made up by Anke use spirit as "fuel" - a magic user transforms the eluding spirit, or some of their personal reserve, into a slightly different form that can be used for manipulations.