Such as "do you like Wikipedia?" "do you trust Wikipedia?" or a honeypot question that would somehow confirm that they understood the previous one.
In order to avoid fatigue, we should only ask one additional question after the user answers the first one. We can randomize what the second question is.
In terms of setting this up, each additional question could be a separate QuickSurvey. We will need some logic for NavigationTiming to be aware that the user has answered the first survey, in order to let it trigger the next one.