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Related to prick up: prick off
1. To rise in sudden attention. Usually said of ears or, less commonly, heads. The dog's ears pricked up when it heard its owner's voice. My head pricked up at the mention of pay cuts.
2. To raise something, especially ears, quickly and suddenly in order to pay close attention. In this usage, a noun or pronoun can be used between "prick" and "up." The antelope pricked its ears up, sensing that a predator was near. Several sheep pricked up their heads as I approached.
3. By extension, to begin suddenly to pay close attention to something. Used in the forms "prick up one's ears" or "prick one's ears up." Be sure to prick up your ears if anything about the case is mentioned. I imagine several federal agencies will have pricked their ears up following the company's controversial announcement.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.