hear the grass grow

verb3

1. •
   To have an extremely sensitive sense of hearing.

   • Heimdall is the watchman of the gods. . . . So acute is his ear that no sound escapes him, for he can even hear the grass grow and the wool on a sheep's back. — 1855
2. •
   To be very aware or discerning; to pay attention to every small detail.

   • He was quick to appreciate Blankenhorn's engaging personality and intelligent use of his skills. Chief among these was a remarkable ability to keep track of developments—to ‘hear the grass grow’. — 1995
3. •
   To hear very well due to being in an exceptionally quiet environment.

   • A suburban arena that was so sepulchral you could hear the grass grow. — 2005