Characters
There’s an eye-opener, and no mistake.
— Sam · The Lord of the Rings: The Fellowship of the Ring
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker reacts to something as an eye-opener, a revelation that sharply changes how things look, and stresses it with no mistake. The phrase carries plain-spoken emphasis: whatever was just seen or learned has shifted their understanding and is not to be doubted.
Context reviewed