Dictation doesn't work

Maybe I'm missing something.

When I double-tap the fn key, the Dictation submenu pops up, and the dots glow once, and they shake side to side. Then it just goes away. It won't let me talk. If I do talk, nothing registers. Hitting fn again does nothing. Why can't I dictate? What's going on, here? I checked my mic in System Preferences, it is registering there just fine.

Help?