"His flashing eyes, his floating hair!" (line 50)
This is the last and most intriguing vision. The speaker dreams he could sing this creature into existence. The dream is turning into a nightmare pretty quickly. It's hard to pin down exactly what we're seeing here. Is this some new vision of Kubla, now ready for war? This person or thing seems to be some kind of god, and whatever is happening with these eyes and this hair, we think it sounds like bad news. This is the part of the dream where you wake yourself up and go have some cookies and milk. Or, you write a poem about it, if you're Coleridge.