Of the curosity in Classical Behaviorism

Classical Behaviorism started by Ivan Pavlov which love to explain any behavior of human being via the construct of Reflex. Thus, his dog will saliva when hunger, and it is paired with a fixed other stimulate such as a ring, the brain would associate the ring with saliva. Thus behavior is all about connecting stimulate and reaction together neurologically. Reflex are, in a sense, similar to classical conditioning since they are both association of stimulate and reaction. The only difference is Reflex are pre-programmed by genes which Behaviorist doesn’t need to explain it at all. It appears in my mind that Behaviorist think they can easily explain any human behavior by fitting into the Stimulus-Reaction framework. However, this framework of explaining human behavior hits a ceiling when it encounter the phenomena of curiosity. Since curiosity is about a novel stimulus, and novel stimulus is what the organism never encounter before. How could natural endowed us with a ‘Curiosity Reflex’ that only react to stimulus which never exists in the behavioral repository? How to program a Reflex when the instruction is ‘For anything you never have encountered before’ since it require potentially unlimited number of unexposed stimulus? Or in his mind, the brain are born equipped with idea of negation, thus we can NOT only condition a behavior with existing stimulus and we can also condition an organism the NEGATION of existing stimulus. How is it possible if the organism is NOT able to do some rudimentary level of abstraction and computation in his/her mental space? Thus the idea of Curiosity Reflex demand the existence of mental space.