prick up one's ears, to

prick up (one's) ears

1. Literally, of an animal, to raise its ears, as upon hearing a sudden noise. The dogs pricked up their ears and started staring outside. I wonder what they heard.
2. To pay sudden close attention to something one overhears. Be sure to prick up your ears if anything about the case is mentioned. I can't help but prick up my ears if I hear someone say my name—even if they aren't talking about me.
See also: ear, prick, up
Farlex Dictionary of Idioms.

prick up one's ears

Listen carefully, pay close attention, as in When she heard them mention her boyfriend she pricked up her ears. This term alludes to horses raising their ears at a sudden noise. [Late 1500s]
See also: ear, prick, up
The American Heritage® Dictionary of Idioms by Christine Ammer.

prick up (one's) ears

To listen with attentive interest.
See also: ear, prick, up
American Heritage® Dictionary of the English Language, Fifth Edition.

prick up one's ears, to

To listen attentively. This term, which alludes to horses holding up their ears at a sudden noise, dates from the sixteenth century. Shakespeare used it in The Tempest (4.1): “Like unback’d colts, they prick’d their ears.”
See also: prick, up
The Dictionary of Clichés by Christine Ammer
See also:
  • prick up (one's) ears
  • prick up ears
  • prick up its ears
  • prick up one's ears
  • prick up your ears
  • prick up
  • get (one's) ears lowered
  • pop (one's) ears
  • lower
  • prick (one's) ears up