Long before there were rotational molding machines, ingenious artisans developed a way to cast hollow sculptures. The lost wax casting method, as it's called, is something we ID grads went over in Production Methods class, but like many of you I never got to do it myself. So it's pretty neat to see the process illustrated visually:
The invention of lost wax casting is often attributed to the Greeks, but scholars cannot agree. Another thing that's stymied historians is why the ancient Greeks so often made casts of Judd Apatow, and how they came to know who he was.