Because of their shape, rivers have often beeen compared to snakes. This refers to the path cut by the Paraguay River, from where it starts in Barzil and while it travels towards the south /southwest from there.

see
http://en.wikipedia.org/wiki/Paraguay_River

where it says
The Paraguay's source is south of Diamantino in the Mato Grosso state of Brazil. It follows a generally southwesterly course, passing through the Brazilian city of Cáceres. It then turns in a generally southward direction, flowing through the Pantanal wetlands, the city of Corumbá, and then running close to the Brazil-Bolivia border for a short distance in the Brazilian states of Mato Grosso and Mato Grosso do Sul.

From the city of Puerto Bahia Negra, Paraguay, the river forms the border between Paraguay and Brazil, flowing almost due south before the confluence with the Apa River.