the answer is: Since Joshua was unable to achieve cognitive equilibrium, he applied assimilation to this new experience
Assimilation is the process of analyzing and incorporating new information around us ( including objects) into our pre- existing knowledge.
At his age, Joshua is in a common period when most infants tend to try to get things into their mouth as their effort to taste and understand the texture of different objects. After trying to do this to the stuffed toys, Joshua understand that he can't do it to this particular object. After assimilating this situation to his mind, he throw the toys away and lose interest.