"Canary in a coal mine" is an idiom that refers to an early warning signal, a subtle but critical indicator that something is wrong or about to go wrong. The phrase comes from a practice used by coal miners in the early 20th century: they would bring canaries into coal mines because the birds were more sensitive to toxic gases like carbon monoxide. If the canary became sick or died, it signaled that the air was unsafe, giving miners a chance to evacuate before the gas levels became deadly. Th...
