How do I split an edge with a key shortcut? How do I split an edge by using a shortcut? I've done it many times, but I've forgotten how I did it.

In picture below, I've done it manually, but I'd like to know how to do it with shortcut.
Select the vertex, face, or edge that you want to rip, and press V.  You then can move the separated vertice(s) around, or right-click (or possibly left-click, if you select with the right mouse button) so that they are on top of each other but not connected.