IDIOMS

look daggers

(idiomatic, often followed by at) To stare in a severe, disapproving, or threatening manner, especially without speaking.

Example: 1835, Washington Irving, Abbotsford and Newstead Abbey, ch. 1:
  Before him sat the grim baron, with a face worthy of the father of such a daughter, and looking daggers and ratsbane.
1912, Jack London, Smoke Bellew, ch. 2:
  Both employers looked daggers at Kit, for the insult rankled.
1986, Stephen Coonts, Flight of the Intruder (2006 edition), ISBN 9781591141273, p. 116:
  [T]wo hostesses approached and looked daggers at Suzy and Teresa, both of whom glared back.