1.   His face hardened momentarily, then he looked away.

2.   Mavis could feel her face harden into a plastic smile, like a plate of gravy skinning over.

3.   His face hardened and he stared down at her with contempt.

4.   He stared at the unfamiliar car for a moment, then his face hardened as he recognised her.

5.   He looked at Caroline like a man rising from a deep sleep, and then his face hardened.

6.   She paused for a second, and her face hardened.