exposed nerve

The unconscious buzzing machine touched the exposed nerve—the silly, absurd, irrelevant name.

It was impossible to think of Freddie without thinking of Derek, and to think of Derek was like touching an exposed nerve.

Sally's heart jumped as if an exposed nerve had been touched.

Annie felt herself jump at this climax, as if she had been touched on an exposed nerve.

Beatrix started, as if he had laid a clumsy thumb on an exposed nerve.