Although it contrasts with the previous mood, it sounds very logical. Sort of like going from yellow to purple. Their very different, but they create a strange and wonderful effect when placed side by side. The rest of the band follows him. They are all playing a little more disjointed now.
Fish however gets the same rhythm going.
Mike sounds a little more sinister, reflecting the darker mood. Quietly, and sounding a little more cooly dangerous. He gets more passionate as time goes on. Fish follows him and gets equally tempremental. Mike and Page can do nothing but join the flow.