1.   Her expression did not change, and she answered me calmly.

2.   She made a face at his back, but her expression quickly changed to concern when she caught sight of his arm.

3.   Her expression changed gradually to puzzlement.

4.   Then suddenly his expression changed.

5.   Even as she was thinking about rallying her defences, his expression changed.

6.   Then, suddenly, his expression changed and he frowned.

7.   And no matter how many landscapes the dog travels to, its expression never changes.

8.   But when he looked across the terminal and saw another boy from the camp, his whole expression changed.

9.   But when he looked up, his expression changed.

10.   Collectively, their expressions do not change from tipoff to final horn.