Behavior is readily classified into patterns of movements with inferred common goals—
actions. Goals may be discrete; movements are continuous. Through the careful study of
isolated movements in laboratory settings, or via introspection, it has become clear that
animals can exhibit exquisite graded specification to their movements. Moreover, graded
control can be as fundamental to success as the selection of which action to perform under
many naturalistic scenarios: a predator adjusting its speed to intercept moving prey, or a tool …