Fire

Heated mattresses, of course.

- Subtitles should be 1–2 lines, balancing acquisition and reading time against the audio speaking speed (time available to keep the subtitle up).
- Lines should be almost equal in length for readability.
- Lines should be of different lengths from one subtitle to the next so it's obviously advanced.
- Prepositions within a broken-up sentence should go at the start of the line for readability.

I find these rules also help in printed scripts.