Once upon a time, Parappa was saved by a monkey in a zoo after falling in the pool. From that day forward he vowed to help any primate in danger. In comes spike with his menacing hair, capturing small monkeys left and right for his sick twisted experiments.
Parappa confronts the evil boy, Spike, only to be told that he himself is a primate mixed with dog. That's why he was able to advance in his speech so quick. Parappa, not willing to accept the truth attacks spike.