How can I choose a user an the login page without a mouse? As a old-school Unix junkie I don't like being forced to use a mouse when a simple keyboard shortcut would do. Today I found myself needing to login to an OSX machine just to launch an app, but the system's mouse had a dead battery. I tried about every key I could think of on the keyboard and could not figure out how to select a user  from the login screen. I could change the system volume and any number of other useless actions, but a keystroke that would change the input focus to the user selector was beyond my ability to guess.

Even more frustratingly, when I did finally hook up a mouse, merely moving it seemed to bring the login window into focus and the arrow buttons could be used to select a user.

On attempting to duplicate this later, it seems the initial login screen does have keyboard input focus and works on first bootup. However if you either wait a minute or two for the mouse connection dialog a dialog pops up wanting you to connect a mouse. This steals the input focus and never gives it back to the login screen. If you do not connect a mouse or if an almost-dead wireless one connects and disconnects, the login screen cannot be accessed from the keyboard.

Is there a key-binding I am missing that will re-focus the login page? Or is one just stranded at that point? Is there a keystroke that will reboot the system so you can catch it before the mouse connect dialoge pops up?
The clue was from activating the voice-over, which eventually tells you:

Ctrl + Option + Shift + Down Arrow simultaneously followed by left/right to choose user, 

You don't need to activate voice over for this to work.

That is completely non-intuitive: a simple tab would solve this completely.