REM sleep's chemistry—acetylcholine surging, dopamine humming—does the heavy lifting of vividness, but the brain still has to make sense of the electrical fireworks. It uses its language circuits to stitch those spikes into metaphoric storylines, like a scriptwriter turning raw footage into a movie. So yeah, the chemistry fuels it, but the metaphors are the brain's way of turning chaos into something relatable. It’s like a dream‑lab where chemistry creates the sparks and the brain’s narrative engine paints the picture.