Nail in the coffin: dispelling the "death nail" myth

What kind of error is it?

Malapropism

Why do people make this mistake?

The error likely arises from confusion between similar idiomatic expressions, specifically "death knell" and "last nail in the coffin". People might mistakenly conflate these phrases due to their similar metaphorical meanings related to finality or inevitable doom.

What is correct?

"Death knell" is the correct expression, which refers to an event or situation that signals the end of something. "Death knell" originates from the historical practice of ringing a bell to announce a death. If referring to the final element that leads to the end of something, "the last nail in the coffin" is correct.