This example shows two different ways in which particles can be crept on a surface. In this case, the surface is a contorted tube.
One version shows how particles are crept inside the surface, the other shows how particles are crept outside the surface. This is done by changing the z scale in the Creep SOP, which offsets the particles perpendicular to the surface.
The particles are birthed from a circle that is carved from the tube geometry.