Why would Morty mention "first part" in this context?

Native speaker’s answer
Rebecca
He mentions "first part" because he's hoping that Rick doesn't stay a pickle, as if a "second part" of a magic trick would turn Rick back into a human! Ex: For the first part of my magic trick, I will disappear. If the second part works out, I'll reappear soon. Ex: Was that the whole story? That was a bad ending. You need a second part.