CTRL+LMB — drag to lasso-select (add to selection). Alternatively, click to perform one of the following actions:
if nothing is selected, a new unconnected vertex is added to the current mesh.
if a single vertex is selected or vertexes on a non-enclosed object are selected, a copy will be created and will be joined to any previously selected vertices by an edge, or edges.
if an enclosed mesh (a cube, etc.) is selected, an unconnected copy will be created under the cursor.
