I'm new to Mac, and I have to say I really like how it handles two-headed displays. It makes it easy to specify where the external monitor is and slide things from screen to screen. It even somehow remembers the different configuration for my home and office setups, so when I'm at work it knows the external monitor is to the right, and at home to the left. However, sometimes I just want to have everything on my big screen, and let the MacBook screen stay dark. I know this is possible because it sometimes happens spontaneously when I wake the Mac up from sleep. How do I make it happen though?