Draw Details Tool

Once you have drawn a curve, you often need to change a small part of it, or add some details. This is what the Draw Details Tool is for.

When you select a curve after creating a new object, the tool cursor changes to , the Draw Details Tool.

You can also activate this tool by selecting a curve and pressing "D", or by choosing it from the Tools Panel.

Redraw a Part of a Curve

Select a curve, (Drag with the RMB until a curve is highlighted in yellow)
Then starting and ending on the curve, re-draw a small part with the LMB.
When you let go of the LMB the curve you drew is blended into the original curve, and the object is rebuilt.
If you want to preserve the crisp details of your curve, you can increase the resolution of the curvy object on the Object Properties Panel. This image shows a higher resolution version of the same model.

Example

You can add a lot of detail to a curve using this tool. It is also useful to help square of corners, and add little ridges or grooves in an object.