The painter's pause

At first the sitter was animated, moving his hands whenever he spoke. After half an hour he became still, following the painter's request to keep his chin in the same position. I had thought the difficulty would belong entirely to the person holding the brush. From a seat beside the door, I could see that the sitter was working too. His task was to make an ordinary posture last much longer than it naturally would.

From the passage, select two words or phrases that describe the change in the sitter's movement.