Strange to me that a group of fisherman who insist that the using correct batch of gun metal gray flashabou is important think that the same genius level trout will eat a swivel instead of their awesome chironomid often enough to matter. Seems that one or another may be true but likely not both.
Then there is size. Couldn’t the size of the swivel be adjusted such that the trout realize that it is the wrong size for the pupae they are eating?
Is it just rainbows that do this? Everyone knows brookies and cutthroats are dummies. Browns are likely too smart to ever hit a swivel.
Further, to follow on what Wayne said, why is it so bad if they do hit the swivel? Is the assumption that the fish would have taken the black, shiny thing with the hook if he wasn’t busy eating the black, shiny thing with no hook?