A well-known chestnut is "People who like laws and sausages should probably not watch them being made." These two things are associated in another way: My German class on Monday is immediately followed by my political science class.
It's long been a puzzling phenomenon to teachers that the results of their informal polls which are conducted by show of hands do not add up to 100% of the students. And these aspiring pollsters sometimes comment on what they see as a logical absurdity, with quips such as "so I guess of the fifty of you, thirty were born inside the United States, ten were born outside the United States, and the other ten... were not born?" (Example made up.)
They're just lacking a good control question. Not everyone present has agreed to participate in a show of hands survey. Not everyone might be paying attention. I think that if you want to poll your audience this way, you're better off if you start with a test question: "Raise your hand if you're willing to participate in a show of hands survey."