expression, ichidan verb
prick up (ears); cock up; perk up
Used specifically for ears standing up or being pricked up, often in response to a sound or alertness. The phrase is a fixed expression combining the mimetic adverb ピンと (straight, taut) with 立てる (to raise).
See also: ピンと
犬が音に気づいて耳をピンと立てた。
The dog pricked up its ears at the sound.
猫は興味があると耳をピンと立てる。
Cats prick up their ears when they are interested.