He looked back at me then, and his expression changed.

He looked away again, and the expression on his face did not change.

Though his expression didn't change, he lost enough color to answer the question she hadn't asked.

He looked at me, and the expression in his eyes changed.

Then she thought of something else, and her expression changed.

Her expression changed, and she really looked at me for the first time.

Her expression did not change, but the idea got across.

When his expression didn't change, she gave him another five.

The expression on his face changed, as he looked at her.

The expression of the man against the wall did not change.