耳みみを澄すます

expression, godan verb (-su)

listen carefully; strain one's ears

Used when one focuses intently on hearing faint or distant sounds.

See also: 澄ます (すます)

• 夜よるの森もりで、彼かれは耳みみを澄すましてフクロウの鳴なき声ごえを聞きこうとした。

  In the forest at night, he strained his ears to try to hear the owl's call.