Select all of the control Points in the 3rd row. Just like before, drag them down untill you have something like this. Notice how you have more control of the surface. Lets say we wanted to put in a small ripple in the surface going verticaly. All we would have to do is insert a knot there, and then move the control points we just added.
Lets give it a try.
Select the surface. Click and add 3 knots close to each other in the middle. In the top view, Drag them down as before. You should end up with sonething like this. This is a very powerful tool that can give you a lot of control and keep your point counts down.