Howard Webb has accidentally set off a can of the new vanishing spray, designed to stop defenders at the World Cup encroaching at free-kicks, much to the amusement of his fellow referees.
"You should be good with that," Australian whistler Ben Williams jokes with his English colleague, a former policeman. "It's just like pulling a can of Mace".
"It's the first time I've used it," chuckles Webb as Fifa's team of referees for Brazil 2014 stop their exercise to mockingly applaud him.
The Premier League referee, who issued 14 yellow cards, and one red, in the 2010 World Cup final between Spain and the Netherlands, quickly gets to grip with a new device that is likely to attract just as much attention as goal-line technology in Brazil.
Used for several years in Brazil and Argentina for domestic football, it was trialled at international level during last summer's Under-20 World Cup, and also featured at the Club World Cup last December.
"You spray a circle around the ball and a line 10 yards [9.15m] away for the defenders," explains Webb as he demonstrates how it is supposed to be done moments later.
"It will assist us in getting the players back at a free-kick and, in turn, that gives the attacking team a better opportunity of creating something from that set-piece."
Webb believes that with defenders no longer able to creep closer to free-kick takers, the spray "could lead to more goals from free-kicks" at this World Cup.
That point is underlined as the referees begin their session and the first free-kick taken with the defenders standing behind the spray curls into the top corner. "Just like Pirlo," Webb smiles, in reference to Italian midfielder Andrea.
The 42-year-old official is making his debut with the new spray can, which referees will hook into a holster on their shorts, but some of his colleagues have used it before, and believe it will prove popular.
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