Well, if they're familiar with beer, and sophisticated enough to pour it into a glass: poured very quickly, the beer will develop a large head that overflows th

Well, if they're familiar with beer, and sophisticated enough to pour it into a glass: poured very quickly, the beer will develop a large head that overflows the glass, but pouring slowly creates a smaller head (or none, but don't do that). There's not more beer, but it fills more space temporarily when poured faster.