Of course, in reality, paint is not infinitely divisible, and at some point the horn would become too narrow for even one molecule to pass. But the horn too is made up of molecules and so its surface is not a continuous smooth curve, and so the whole argument falls away when we bring the horn into the realm of physical space, which is made up of discrete particles and distances. We talk therefore of an ideal paint, in a world where limits do smoothly tend to zero well below atomic and quantum sizes: the world of the continuous space of mathematics.