Hello, all the boys send you a greeting.

The beverage is called "MATE", and is an infusion that is prepared with "Yerba" (is a Herb, like "te") is put in a hollow pumpkin and drought, called "MATE". It is drunk through a "bombilla"(hollow slender tube used to suck up liquids). 

You can get more informacion in:
http://www.rau.edu.uy/uruguay/cultura/mate.htm
http://www.brounet.com.uy/Novedades/Museo/gaucho/elmate.htm

Saludos,
Sergio.