hackle

In its earliest uses in the 15th century, hackle denoted either a bird's neck plumage or an instrument used to comb out long fibers of flax, hemp, or jute. Apparently, some folks saw a resemblance between the neck feathers of domestic birds—which, on a male, become erect when the bird is defensive—and the prongs of the comb-like tool. In the 19th century, English speakers extended the word's use to both dogs and people. Like the bird's feathers, the erectile hairs on the back of a dog's neck stand up when the animal is agitated. With humans, use of the word hackles is usually figurative. When you raise someone's hackles, you make them angry or put them on the defensive.