You might have seen the mural in La Trobe Street – a stretch of wall near Swanston Street painted with sad grey battery hens wearing fast food boxes over their heads: a sly shot at the burger chains, the submarine sandwich sellers and the peri peri chicken grillers. A hashtag in one corner, #fixfastfood, clues you in that this must be some activist statement about factory farming – a quick throw-up by a guerrilla animal rights group.