turn a hair, not

not turn a hair

To show no outward emotion when something bad happens or is announced. I thought he'd be devastated after losing the race, but he didn't turn a hair. You have to give Jane credit: she didn't turn a hair when the customer started shouting in her face.
See also: hair, not, turn

turn a hair, not

Not become afraid or upset, remain calm, as in She didn't turn a hair during the bank robbery. This term, also put as without turning a hair, comes from horse racing. After a race, a horse often has roughened, outward-turned hair. Its figurative use, nearly always in the negative, dates from the late 1800s.
See also: not, turn