When Pi was "talking" to Richard Parker, it proved that we was on his last leg of the journey. Only when he began to go officially insane, only then did he really die mentally. His dream rag was only a prelude to his insanity.
At first, when Richard Parker spoke to Pi, he was almost stunned. He awoke thinking he was talking to someone and his hopes raised. But were only killed slightly when he realized it was the tiger. Slowly, Pi began to descend into the conversation with much thought, focus, and expression. He began talking about food, the only thing on his mind. Richard Parker began asking about the foods Pi was interested in, expressing his own excitement. It shows a little desperation in Pi, thinking that his only companion is as interested in the things he is, when in reality, many people couldn't care less about your likings. As the conversation deepens in thought and expression, Pi begins to accept the fact that a Bengal tiger is talking to him from beneath the tarpaulin! Now, he has crossed the border. Now, he has passed the point of no return. He can no longer regain sanity unless he is shaken up by reality.
To be shaken up by reality, he has to hit it like a boat hitting the shores.
