In addition to the Surface Lasso, you can draw traditional 2D lassos. You begin a 2D lasso by pressing the left-mouse down somewhere on the background, not on top of the selected model. This initializes the lasso.
There are two modes to the lasso:
- Click-and-hold to create a free-form lasso that follows the cursor that will complete when you release the mouse.
- Click-and-release to begin a polygonal lasso, and each additional click will add vertices to the lasso, until you complete it by clicking again on the starting point.
In the polygonal lasso, the resulting selection will be all triangles whose vertices are fully within the lasso. However in the freeform lasso, the curve does not have to be closed, as shown on the right. In this case you can think of the curve as "cutting" the model into two sides, and the selection is determined as the side which has the smaller number of faces. This may sometimes select the "wrong" side, which you can quickly correct with the Invert (i) or Invert Connected (shift-i) hotkeys.
By default, each time you draw a screen-space lasso, it will replace the existing selection. Holding the Shift modifier while drawing the lasso appends to the current selection, while holding Ctrl/Cmd deselects.