An environmental graffiti artist in Brazil went into a tunnel and began washing the walls of the grit and grime created by millions of tons of pollution created by automobiles passing through the tunnel.
But instead of simply washing the walls, he “etched” skulls with his washing. That is, he drew skulls on the wall with water and rags – nothing destructive and nothing that could cause him to be arrested.
Check it out. Especially at the end where authorities, outraged by the artwork, went ahead and washed all the walls. Heh.
[Source: Environmental Graffiti]