Palette cycling
Animating an image by rotating the entries in its colour palette instead of redrawing a single pixel.
On indexed-colour hardware a pixel points not at a colour but at a slot in the palette. Swap the contents of those slots and every pixel aimed there changes at once, without touching the image memory. Put a run of colours in a loop and step it one place per frame and something appears to flow: waterfalls, lava, rain, running lights. The animation costs almost nothing — just a write to the palette registers.
The trick flourished through the 1980s and 90s. Mark Ferrari pushed it furthest in LucasArts backgrounds like Loom and Monkey Island, where still scenes seem alive purely through palette motion. Don't confuse it with palette swap, which recolours a whole sprite to make a variant. Today it is mostly a retro flourish, but it survives in pixel-art tools.