So we usually don't recognize we're dreaming.
Sharks fly by, teeth fall out, you're back in school (and probably late for the test), the room fills with water. Wait! you think. Is this a dream?...
A chimney dances a jig. A fireplug melts.
It seems that there are some tests you can run, mid dream, that give more reliable answers. I snagged them off Wikipedia's article on Lucid Dreaming.
- Read something, look away, and read it again. Letters change in dreams.
- Flip a light switch. In dreams, the light usually stays on or off.
- Try to stick your finger through the palm of your hand.
- Look in a mirror. Dream reflections are wonky
Maybe I'll try them.