When you use the Lasso tool and its Polygon Mode modifier, you can switch between the freehand and straight-edged selection modes.
Draw a freehand selection area
around
the area.
Draw a straight-edged selection
area
in
the options area of the Tools panel.
Draw a selection area with both
freehand and straight-line edgesRelease the mouse button; Flash will close the selection area for you.
Double-click on the starting end of the selection area line.