I looked up the drink recipe from several sites...Lager (beer), Cider (doesn't say so but I assume hard cider) & top with black currant cordial. I guess it foams & chemically reacts in very strange manner. I read many European pubs refuse serve it...
1. Knocks people on their ......
2. They don't like mopping up the vomit...
3. It attracks the "goth" types because of the thick, cloudy, bloody color...