Boot into Mac OS X Verbose Mode
You can boot into Mac OS X verbose mode just once by holding down Command+V immediately after powering on a Mac (or immediately after reboot). You’ll know you’re in verbose mode because you’ll see lots of text reminiscent of the command line rather than your standard Mac OS X boot screen.
Verbose mode can be useful when troubleshooting Macs and developers often use it too. The standard user probably has no need to be in verbose, but it can still be fun to look at the underpinnings of Mac OS X. If you just hold down the key combination, your next reboot will be normal again, but you can also set your Mac to always boot in verbose mode.