The long feathers on the neck of a bird, especially a rooster, or the hairs on the back of an animal's neck that stand up when angry or afraid.
From Old English 'hackle,' possibly related to 'hake' (a hook-like tool). The word originally referred to a tool for combing flax or hemp fibers, then came to mean the neck feathers of birds that resemble the comb.
When you see a rooster's hackles puff up during a fight, you're watching millions of years of evolution—those feathers make the bird look bigger to intimidate rivals, a trick shared by countless animals from cats to porcupines!
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