USING THE LASSO TOOL? KEEP IT STRAIGHT

We normally use the Lasso tool (L) for drawing freeform selections, but sometimes you'll find that while drawing your selection you'll need to draw a perfectly straight segment, even for just a few pixels. You can do just that by holding the Option key (PC: Alt key), releasing the mouse button, and continuing to draw your selection. You'll notice that your cursor changes to the Polygonal Lasso tool, and that as you move the mouse, a perfectly straight selection will drag out. When you've dragged the straight selection where you want, click-and-hold the mouse button (to add a point), release the Option/Alt key, and you'll be back to the regular Lasso tool again. Drag the mouse to continue drawing your selection.