El Sapo - The Frog

Sometimes when you are traveling by bus in Chile, you will see a man (that is usually standing in the middle of the street) shout some numbers at the driver, who will in turn give him a coin or two. The numbers that he shouts are in fact the number of minutes that have gone by since the last bus from the same bus line or going along the same route. These men are called Sapos and earn a living (though illegally since it's not permitted for tax reasons) by writing down the time every bus goes by that part of the street and calling out the numbers to them.

Why do they do it? So that the driver knows whether there is a bus a short distance ahead that could be taking any potential clients. If there is, they will usually speed up to try and overtake it. In Chile, the bus drivers apart from those that work for Transantiago don't receive a fixed salary. They receive a small percentage of every passenger they take, hence the race against time and other buses.