 But for Pereira it was evident that, before the same object, the behavior of an animal could vary and even be contradictory. He explained such a variety by resorting to a complex interaction of factors that occur simultaneously. To illustrate this question the author described the case of an animal that on some occasions drinks as a reaction to the presence of water and on other occasions does not, depending on the interaction between the species produced by the water and the current internal state of thirst of the animal (AM: II.877).