Weird Train Scene

"Suicide Club" is one of those movies that leaves you utterly perplexed. The title says it all, but you don't expect the action to take place since the very beginning.
The opening scene takes place in a subway, apparently during rush hour. The camera focuses on a group of students who just came out of class. The mood is quite chipper, especially with the silly music playing as a background. When the train approaches, the students line up holding hands and counting. There's not really much to think about, nothing to be expected. They're just happy teenagers singing and being foolish, waiting for their ride home just like everybody else. Then splash! The line of uniformed girls jumps into the tracks and waves of blood soak everything, the bystanders, the walls, the shop keeper, the train, EVERYTHING. Talk about an unexpected scene! It's disgusting!