quail at (something)
To become fearful of, nervous about, or averse to something; to avoid or shrink from something. I know that David quails at the thought of flying in an airplane. We quailed at the notion of shutting down the company that our great-great-grandfather created. We can't have you leading the team if you're going to quail at the first sign of difficulty.
quail at someone or something
to show fear at someone or something; to shrink from someone or something. Todd quailed at the thought of what he had to do. The students quailed at the teacher who had been so hard on them in the past.