Specular aliasing
The flicker in specular highlights that appears when a surface carries more normal detail than pixels — the glint "boils" the moment the camera moves.
A glossy surface concentrates light into a small, sharp highlight. When the surface normals vary faster than the screen can sample them — a fine normal map seen at distance, or a near-mirror material — the highlight lands on a pixel one frame and misses it the next, and the result is a restless sparkle in motion.
The cure is to couple normal variance to roughness: when a mip level is averaged down, the spread of the normals should raise the roughness value, so the gloss softens as the detail disappears. The Toksvig factor and LEAN/CLEAN mapping do exactly this; temporal anti-aliasing mops up the rest by blending several frames. The problem is worst on metallic and glossy materials.