Every day at 9 in the morning and 3 in the afternoon, the people of Paraguay take a collective pause for tea. This tea is called Tereré (te-re-ray) and is made from yerba maté (Yerba ma-tay) which is a species of holly.
Everywhere you go, people carry with them a water thermos and their tea supplies. It's the equivalent of the latte in American culture.
There is quite a rich culture surrounding this tea, the most important of which is the invitation to and solidification of friendship. Paraguayans are extremely friendly and accepting.
The tea is served out of a guampa (gwam-pa) and taken through a bombilla (bom-bee-ya) which is a metal straw with a strainer at the end of it. The host fills the guampa with tea, then nestles the bombilla down to the bottom. Water is poured over the tea and taken through the bombilla. You should drink until the tea "talks" or makes a little slurp as it is considered uncouth to leave water in the guampa.
The server (normally the host) takes the first drink because the tea is somewhat bitter in the beginning. After that, if there is a person of importance present, they would receive the second drink, followed by the next person in clockwise fashion. If you didn't already catch on, everyone shares the same cup and straw!
It is considered rude to refuse the tea when it is offered. Remember, it's not just a tea, it is a sign of friendship. After two or three rounds, you can finish without giving offense. A simple "gracias" lets the server know that you are through and he will skip you through the rest of the visit.
Traditionally, tereré is not mixed with food, though certain sectors of the culture do regularly eat a snack with their tea. We were advised that it is good to eat a little snack just before you drink Tereré to give a "shelf" for the tea "to rest on" in your stomach. Tereré should never, ever be mixed with watermelon - though I haven't been able to find out exactly why that is! :)
While 9am and 3pm are the "recognized" times, there's never a bad time for a tea break, especially in this hot climate! I personally find Tereré refreshing, especially when enjoyed in the company of good friends!