Are they spraying shaving cream on the pitch?

Hello, you either have JavaScript turned off or an old version of Adobe's Flash Player.

WORLD Cup viewers around the globe are asking the same question right now: what is that magical vanishing spray the referees are using on the field?

Referees are using a spray similar to shaving foam to stop defenders from edging closer to the ball during free-kicks in Brazil.

Japanese referee Yuichi Nishimura sprays a line after calling for a free kick during the World Cup opener between Croatia and Brazil. Source: AFP

The ref sprays the water-based foam in a circle around the ball, walks 10 yards and sprays another line that the defenders need to stand behind.

Then, magically, the spray vanishes.

Well, maybe not magically. The can contains water and butane gas. The butane expands when the pressure changes and quickly evaporates, leaving just the water on the ground.

Ivorian referee Noumandiez Doue sprays a free kick marker on the pitch during a Group B football match between Chile and Australia. Source: AFP

Players, constantly looking for any advantage they can get, would often encroach on the 10-yard area they are supposed to stand behind, but this measure allows referees to police the problem much more easily.

The product has been used in domestic leagues in Brazil and Argentina but is making its first appearance — and disappearance — at international level.

Referee Wilmar Roldan sprays the temporary line for a free kick as Benjamin Moukandjo and Enoh Eyong of Cameroon form a wall. Source: Getty Images

Australian referee Ben Williams joked it was like "pulling a can of Mace", while English official Howard Webb suggested it could lead to more goals being scored from set pieces.

"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 told the BBC.

Unsurprisingly, the spray has become a hit on social media. A Facebook page is dedicated to it and there is no shortage of memes.