Paying on the bus

Something I've noticed when going by bus in Medellin is the manner how people pay. After quite a bit of bus rides, I felt I was the only one pulling out my wallet when entering the bus and paying. So I started observing people and saw that almost nobody ever showed their wallet (or don't they have one? I am not sure). When entering the bus, people just mysteriously pull out a couple of bills from their pocket, just enough to pay the ride (the fee is about 1700 pesos, around 1 US dollar).

I started wondering, do they prepare and count those bills at home, or do they do it secretly around the corner before reaching the bus? I am still not sure. To reduce any risk and melt into the culture I thought I would start preparing my bus ride already at home, counting some bills and coins, but I constantly forget it and when I enter the bus I still need to pull out my wallet. Foreigner!