woundered this myself
saw a head modeling tutorial where the plan was to place curvey lines across a poly i couldnt think of a way to do it other than to place intersections at all turning points as above ... but i got the idea that that was not the plan ??? would love to know if there is way as it would empower the process heaps what with puting loops where you want them to startwith etc.
"Climbing the walls of the 'Uncanny Valley"