At least 2 ways: 1) In hindsight. Usually the truth/details eventually become available. This reqires them to be observant/curious enough to notice. 2) By bri

At least 2 ways: 1) In hindsight. Usually the truth/details eventually become available. This reqires them to be observant/curious enough to notice. 2) By bring close enough to the news item to have the story contradict your knowledge. This is how it worked for me, and made me dig deeper. Working against both of these is Gell-Mann amnesia and a general lack of attention.