There is apparently a civic regulation in Rio about noise.
At any given time, two of these three sounds must be driving you insane – pointless car honking, yipping police sirens and improperly muffled motorcycle engines.
Usually, in order to stay well within legal parameters, it's all three.
Then, late afternoon, you feel a tingling. Your lizard brain has begun flashing a warning message: "Something has changed." You get up out of your seat and head to the window.
And, outside, nothing. No cars. No people. No sound. Welcome to the Zombie Apocalypse, and you without your shotgun.
This happens in every city when the home team is playing a big game, but I have never felt quite the same eeriness as in Rio, which otherwise throbs until all hours.
Every few minutes, a single car will pass. And you'll think, "For your sake, you better be headed to the hospital."
Then, Brazil will score. Neighbourhood-wide cacophony from every direction. Side to side. Up and down. You have broken down the aural fourth wall.
It isn't just screaming, but horns and firecrackers. These are not firecrackers from back home. This is decommissioned military ordnance. You can feel these things going off.
Residents were in a proper celebratory mood long after Brazil defeated Cameroon 4-1 to advance to the Round of 16 on Monday night. One wonders why.
On the ground and, crucially, away from the arenas, the tournament has been great fun to this point. Unlike recent hosts South Africa and Germany, Brazilians care about all the games here, rather than just their own. Cafés and bars are packed from early afternoon until well into the evening with patrons watching football. If you brought a ball out onto the street and began kicking it against a wall, a crowd would gather.
Yesterday, our cab driver was watching South Korea-Algeria on a small dashboard television. In the car. While he drove. On the highway. Very poorly.
I don't mind dying. I've lived well. But please, not for South Korea-Algeria.
All this augurs well for the next three weeks because you're beginning to get the strong sense – growing steadily into a certainty – that Brazil isn't headed anywhere here.
They're great individually. The bench players could form a Brazil B-team and squeak into a World Cup. But they are not very good together, in any combination.
When the ref piggybacked them through a tough opener with Croatia, you thought, "Okay, first game. They're nervous. This will all come together."
During the second game, when they were stonewalled by a Mexican goalkeeper so highly regarded that he is currently unemployed, you thought, "Unlucky. A bit snakebitten. This will all come together."
But throughout much of their game against Cameroon, possibly the worst of 32 teams in the tournament, they looked even worse.
They started strong. Within the first two minutes, forward Fred had a point-blank chance. Predictably, he missed. (Parenthetical: Brazilians pronounce Fred as "Fredge." Now that you know that, you will not sleep for three consecutive nights.)
Having failed to score at the first opportunity, they downshifted to first gear. Suddenly, maddeningly, this was a real game.
It wasn't until Cameroon's Allan Nyom decided to lazily shove Neymar into a bank of photographers at the end of the pitch that the Brazilians woke up. And by "they," I mean just Neymar.
The real lesson of the first three games is that Brazil doesn't have a world-class team; it has a world-class player. Only Neymar has the invention we associate with great Brazilian creators. He is a whippet-thin, brazen scamp who plays the game inside his own mind. His teammates are trying to think their way through problems, and failing. Neymar doesn't require plotting. He only needs his instincts.
He scored the first goal – a beautiful turn of the boot that looked far easier than it was. Panic averted. After a distressingly long stretch of dominance, Cameroon equalized. Panic back on.
Neymar scored the second, as well. Panic averted. Brazil added a third. Relief dawning. Suddenly, in the other, simultaneously played group game, Mexico was up on Croatia 3-0. Panic back on.
Had Mexico scored again, they'd have topped the group on goal difference. But Brazil added a fourth, long after Cameroon had checked out of the contest. Panic finally choked out.
Before the day's events, the news here focused on complaints by Netherlands manager Louis van Gaal. The Dutchman was in high dudgeon that his team, in Group B, would have to play before Brazil and Group A. He suggested that Brazil could use the advantage of knowing the results from the other group to choose their second-round opponent.
Van Gaal didn't quite use the word "fix," but it was floating around the edges.
This wasn't fear. It was gamesmanship.
Based on form, if the Dutch were to play Brazil right now, they'd annihilate them. Before the tournament started, Pele claimed that this was the most defensively sound Brazilian team ever. That pronouncement now looks laughable. If you go straight at them, the Brazilians cannot stop you.
After all the wretched, wretched math was toted up, the hosts will instead face Chile in the Round of 16. That has the strong look of an upset.
You never do know. Teams sometimes click once they reach the knockouts. France looked equally miserable through the group stage of World Cup 2006, and then made it to the final. On this stage, chemistry is more art than science.
But one has a premonition of the recurring, countrywide silence this coming Saturday afternoon. That silence may stretch on long after Brazil has finished playing.