@blogdiva One of the problems with touchscreens and ballot marking devices (the kind evidently used in this Tennessee county) is that there is no way to distinguish a machine error (or malicious machine behavior) from an innocent mistake (voter touched the wrong place on the screen, etc). And in practice, it's almost always the latter. So no individual case is a "smoking gun".
But it underscores how critical it is for voters to check the paper carefully!