During the manufacturing boom of the late 19th and early 20th century greater urbanisation led to high intensity housing. Cities like New York built tenements with the apartments built one on top of the other. The walls and floors were rarely sound proofed and it was normal to overhear others in the tenements. With shift workers people were getting up and going to bed at different times and for those sleeping hearing shoes bang the floor above was common place and often a source of irritation. Groggy neighbours remained awake until he heard the other shoe drop. The tenant in the upper apartment would remember that he had a sleeping neighbour below, and take the second shoe off and carefully place it on the floor, making no noise. The neighbour below in frustration would yell, "For God's sake, drop the other shoe!" The anticipation for the other shoe to make a similar sound was created. Waiting for the other shoe to drop became a popular phrase by the 1940s and was used in common vernacular when someone was expecting something to happen following a specific occurrence and with certain inevitability. In an early cartoon of Hitler, the dictator was depicted with a shoe over the top of his head and the caption "waiting for the other shoe to drop."