Most of the, not necessarily dumb, remarks I have heard have been around the air we breath. Most people think that we breath pure oxygen, not compressed air. Many times I have heard on the news the expression "oxygen tanks" along with some news items in the newspaper. Others find it odd that the air only lasts for about an hour. Some think that we can go down hundreds of feet and stay there on one tank. Of course, I believed the same things before I took up diving myself.