the world > animals > by habits or actions > habits and actions > [verb (intransitive)] > raise the bristles or hackles (3)
To bristle up as an excited beast, raise the mane.
Of an animal: to raise the bristles, as a sign of anger or excitement.
intransitive. Of an animal: to raise the hackles, usually as a sign of warning or fear. Also of fur or hair: to stand up. Frequently with up.