FUN WITH IDIOMS

This article contains three interesting idioms: to sound the alarm, to put the last nail in the coffin (of something) and a canary in a coal mine.

To sound the alarm means to give a warning (that something bad is going to happen).

The last (or final) nail in the coffin (of something) refers to the final event (in a series of events) that causes something bad to happen. (In the story it means the final piece of evidence.) A canary in a coal mine is an especially interesting idiom. In the old days, coal miners would take canaries with them into the mines. If the canary died it meant there was insufficient oxygen or some kind of poisonous gas in the air. This was a warning to the miners that they should leave the mine immediately.