He still has a Boorah gubberrah, a sacred stone, inside him, hence his strength.
He sets string traps for men, touching which they feel ill, and suddenly drop down never to rise again.

The wirreenuns know then that Nahgul is about.

They find out where he is.

Circling, at a good distance, the spot he is on, they corroboree round it.

Hearing them, Nahgul comes out.