Literary ploys - you, me, Dr. Watson and Captain Hastings
It is the "Dharma" of the Watsons and Captain Hastings of the world - whether vegetarians or not - to swallow all red herrings proffered by the gifted sleuth. That is the time-honored prescription for all wannabe celebrity mystery writers.
In so doing, the Watson s and Captain Hasting s capture and retain the interest of the ordinary readers with a "yeah-I-too-was-wondering-about-that" kind of feeling, and make sure they keep on reading.
Then comes the snub from the superior intellect, just as the reader was feeling vindicated because Dr. Watson or Capt. Hastings spoke the reader's mind!
Yet such a empathetic and proxy representation of the reader also protects him from feeling snubbed when a Poirot or a Sherlock points out the "oh-so-obvious-now-that-you-explained" errors of the sidekick. In the process, it also adds some extra luster to the eventual brilliant denouement that comes up in the last chapter. The readers then feel more inclined to go buy the next book.
IMO, the best examples of such literary tricks of the trade can be found in abundance in the book "Murder on the Links". Highly illustrative examples of inadequate application of Aristotelian Logic by Captain Hastings, when he makes determined attempts to show M. Poirot that Hastings himself is no mean intelligence.
Can we think of some more Christie titles as examples?