How to use the smooth tool in weight paint mode? I'm curious as to what I need to do to use the smooth tool in weight paint mode in Blender. The notice says: 


  Vertex select needs to be enabled in weight paint mode.


Great!  How does one enable vertex select in weight paint mode?
The vertex select can be enabled in the 3D View header -



With vertex select masking enabled you can use Shift-Click to select/de-select each vertex from the mask. You can also go into edit mode, select the desired vertices then go into weight paint mode.