His easy-going look suddenly turned sour and his tone hardened.

Suddenly, the tone of the on-line negotiations hardened, according to the court documents.

"Did you tell him" - Griff's tone was hardening - "that it would be too late, then?"

But as the revolutionary mood grew, her tone hardened.

He plodded towards Reynolds, and his tone hardened almost imperceptibly.

But when challenged, his voice quickens and his tone hardens.

Sisko's tone had hardened, the baseball now being clenched in his hand.

His tone had been steadily hardening, and now he whirled on the king and exploded.

Moving on to welfare benefits, his tone hardened.

He briefly looked sympathetic, then his tone hardened again.