hear the grass grow

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.

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

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’.