I do not mean to insult your sister, but there was a study some months ago I think was posted to HN which pointed out that smart, informed people tend to doubt

I do not mean to insult your sister, but there was a study some months ago I think was posted to HN which pointed out that smart, informed people tend to doubt their knowledge a lot more than stupid, ignorant people. From my own experience, I agree. Those who know little seem to jealously guard what they do know and try to overstrech it to suggest they know more than they do. She was probably just thinking "jeez, who cares how manatees float".