It's like that horrifying scene in World War Z when zombies are just on top of each other. It's like a mosh pit that never ends for all of eternity. It's a human traffic jam with absolutely no room to breathe.
It's the train network in Sao Paulo after a bus strike. And the World Cup hasn't even started yet.
There are many train networks in other countries (China, I'm talking about you) that deal with this type of human chaos on the semi-regular basis, but it doesn't change how completely shitty it is to go through.