It might happen anyday, for all a foreign person knows. It would look like a normal day in a normal town; if it's a weekday people would be busy, if it's a weekend, our hypothetical foreign person would probably be stricken by the calmness. The many national flags hanging on windows of homes and cars would be a telling clue, but if our foreign person is American he or she wouldn't even notice. There would be certain nervousness, anticipation if you like, but with such laid back people I understand, it's really hard to detect.
Then, just like that, the streets would be absolutely empty. No cars, no pedestrians, probably no public transportation either. Our foreign person would wonder if there is going to be an attack and people are told to stay indoors. The same streets that 10 minutes ago were bustling with activity (or so it would seem now) are now desert. Some stores might be closed, with no apparent indication on whether it's their normal opening hours or they just went out of business.
After a while, the silence gets oppresive. Not a wailing siren of an ambulance or fire brigade, no obnoxious neighbors pumping up the jam, just an elderly lady crossing the street and a beggar sitting on the corner with his dog. The day might be cold, but not that cold. It isn't a national holiday, our foreign person knows for sure because he or she checked that before. It might...
Suddenly a deafening sound erupts, and it's mostly human voices. Cars blare their horns, there might be some firecrackers, a glimpse of people holding each other in elation. Silence again, and a while later mayhem breaks out and people take over the streets. A foreign person would probably wonder what great thing the locals are celebrating, and probably would find the answer quickly.
The foreign person has just witnessed one Fifa World Cup gameday in Montevideo, Uruguay, in June 2010. The Uruguayan national squad was unbeaten during the four games it played during that month, and regardless of what's in store for it in July, it's quite a solid reason already to celebrate. Which is what they do.
It is what we do while it lasts. May it last a long time.