The smudge tool uses the current brush to smudge colors on the active layer.
The Opacity slider sets the transparency level for the paint. A higher opacity setting results in more opaque paint and a lower setting results in more transparent paint.
The Pressure Sensitivity section sets whether hardness or rate will be effected by pressure for input devices that support this option.
The rate slider sets the strength of the smudge effect.
Default Keyboard Shortcut: Shift-S
The Shift key places the smudge tool into straight line mode. Holding Shift while clicking Button1 will smudge in a straight line. Consecutive clicks will continue smudging in straight lines that originate from the end of the last line.