First of all - my German, well, old Germam teacher (he wasn't German btw) used to live in Berlin. And he was amazed, when he ordered a Pils, that the barman filled it to a certain point, then put head on it. And left it for 5 minutes. He says it's something to do with the glass pushing the head upwards, and the fact that it's so thick meaning it can go up and up and up.

Anyway, he had a friend over for a bit. And they went into a Pub, and ordered a Pils. And the friend was amazed at how long it took. And when it was done, he whipped the head off, slapped it onto one of those tray things, and drank the Pils straight down. Apparently the Barman was so livid that he went purple with rage.