How does Agatha Christie use imagery in Curtain?

Imagery:

Crippled with arthritis, he propelled himself about in a wheelchair. His once plump frame had fallen in. He was a thin little man now. His face was lined and wrinkled. His moustache and hair, and hair, it is true, were still of a jet black colour, but candidly, though I would not for the world have hurt his feelings by saying so to him, this was a mistake. There comes a moment when hair dye is only too painfully obvious. There had been a time when I had been surprised to learn that the blackness of Poirot's hair came out of a bottle. But now the theatricality was apparent and merely created the impression that he wore a wig and had adorned his upper lip to amuse children!”