When Tate Liverpool held the first UK retrospective of Paul McCarthy's work two years ago, it issued an adults-only warning. This was understandable, since during many of McCarthy's videobased performances, he variously attempts to fornicate with a jar of mayonnaise, rubs tomato ketchup (a favourite motif) over his penis, lavishes melted chocolate over his bottom and excretes raw sausages, which he then proceeds to eat.