system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do "Mood Rings" work, and where did they come from?
gpt
When the first discovered liquid crystals (the stuff that we now use for LCD displays) back in the 1970s, we weren't really able to do much with them.  The first application was to use them as thermometers.

A mood ring is just a ring that measures your body surface temperature.  There's no real meaning behind it but, back in the 70s, people were into all sorts of New Age bullshit and they became a major commercial success.