Ok, my question arises after seeing this Youtube video (you need to see it to understand what I am talking about): This may be a part physics, part chemistry question. Now, I know that ethanol and water are miscible. I also know that in whiskey, you find both ethanol and water. How come, therefore, when he performs the trick in question such a 'swapping' occurs? Is it because the difference in density somehow overrides the 'diffusion' of the liquids or something?