Then you fall down as the bus jerks away while you're still standing. The buses go on routes around the city, traveling from one end to the other. Santa Marta is like a giant horse shoe with the center a mountain that only people in shanty towns live in.
The man standing in the doorway is not waiting to get on or off, he's the... portero for a lack of a title. He lets you on and takes your money, and when you want to get off, you have to let him know and he lets the driver know.
The drivers always have minimal interaction with the passengers. Mostly, they accept big bills from the porteros and literally sit on them.
In the hand you can't see, he has money clasped between his fingers like a fan so that he can give change without digging through a bag o' money.
The buses' goal is to get ALL the people who want to take a bus, even if they aren't going to the same place. In this respect, the portero is also a sales person. He'll lean out and you'll ask if he's going where you want to go and he'll say yes, regardless of whether he is.
Big buses have their porteros get out and walk alongside where there are lots of people waiting. I've seen one sound more like a salesman than a money collector.