He took a drink and couldn't hide his reaction.

I lowered my head to hide my reaction to her words.

That surprised Picard and he made no effort to hide his reaction.

Holly had hidden his reaction to the whole experience pretty well.

They're aliens, Kirk thought, trying to hide his own reaction to the knowledge of how close to death he had been.

Matt shrugged, trying to hide his reaction to her proximity.

He breathed a slow sigh of relief, hiding his reaction from the others.

Now it was Spock's turn to be startled, though this time he did a better job of hiding his reaction.

At least if you know what to expect, you may have some chance of hiding your reaction.

Jack was appalled, but he tried to hide his reaction.