It took four years to "refine" the Nazi art criteria; in the end what was tolerated was whatever Hitler liked, and whatever was most useful to the German government from the point of view of creating propaganda. A thorough head-hunting of artists within Germany was in effect from the beginning of the Second World War, which included the elimination of countless members within the art community. Museum directors that supported modern art were attacked; artists that refused to comply with Reich-approved art were forbidden to practice art altogether. To enforce the prohibition of practicing art, agents of the Gestapo routinely made unexpected visits to artist's homes and studios. Wet brushes found during the inspections or even the smell of turpentine in the air was reason enough for arrest. In response to the oppressive restrictions, many artists chose to flee Germany.