You could get a pint of nothing but head as well, if you wanted.

In Spain they try to create the head by dumping the beer in the glass, Guinness style, and letting it excessively foam up. So it's half flat and half full.

Same in Germany. In Belgium, the glasses don't have a line and they don't fill them to the brim neither! The only thing that prevents pubs from cheating you out of some of your beer is their reputation. And to be honest, I sometimes had doubts about getting all that I paid for.