bat an eye

bat an eye or bat an eyelash  {v. phr.},  {informal}
To show surprise, fear, or interest; show your feelings. — Used in negative sentences.
When I told him the price of the car he never batted an eye.
Bill told his story without batting an eyelash, although not a word of it was true.
Compare: STRAIGHT FACE.
Categories: informal used in negative verb