The conundrum of the behavioral sciences is that they are not exact sciences in the same sense as physics or mathematics. Behavior is like the spectrum of light: it is as difficult to say when yellow turns into orange as when one behavior turns into another. It is a continuum of quantity, perceptible throughout its duration, describable only when quantity turns into quality.
Friendly, insecure, pacifying, submissive and fearful behaviors are a continuum of quantity, as are content, self-confident, assertive, dominant and aggressive behaviors. The distinction between any two behaviors is a matter of function; the borderline separating one category from the other is a matter of observational skill, contextual parameters, and convention; the way we understand it all is a matter of definition.
Our brain likes to tidy up its stored information in small boxes, but once in a while, I like to turn them upside down. It’s good mental exercise, I find, and helps me keeping a good sense of perspectives.
If animal behavior fascinates you, you will enjoy "Ethology—The Study of Animal Behavior in the Natural Environment," the book and course by ethologist Roger Abrantes.