1.   His expression remained flinty and quite unreadable.

2.   She glanced sharply at him, and although his expression remained inscrutable she had the fleeting impression that his reasons involved a woman.

3.   Her eyes widened involuntarily as she felt the virile power of him against her, but his expression remained unchanged.

4.   All the while, her facial expression remained unchanged.

5.   Daniels offers a sympathetic portrait, but his expression generally remains as impenetrable as the one on the dollar bill.

6.   Expressions can communicate emotions faster, more subtly and more effectively than words, which is why facial expressions remain crucial for humans as social animals.

7.   Some expressions remain so useful that they stay embedded in the language.

8.   Some such expressions remain so dear to writers that they endure as cliches even though they are now so dated that they purely mystify readers.