He transferred the Camels from his overcoat to a jacket pocket. He wondered, as he did so, if they did not represent an unnecessary note of strain. Mrs. Barrows smoked only Luckies. It was his idea to puff a few puffs on a Camel (after the rubbing-out), stub it out in the ashtray holding her lipstick-stained Luckies, and thus drag a small red herring across the trail.
What does "note of strain" mean?
What's more, may we say "drag a small red herring across the trail" equals "mislead others"? Context