The image cannot hold its surface.
On this genus
A body persists while its appearance won't settle. A face changes its features, fabric crawls across a torso, an identity flickers on and off a moving body. Each image may work on its own. The failure appears in succession.
The body carries its motion from one frame to the next, but the model makes its surface again each time. Pose and movement continue while texture, detail, and identity change around them. The surface stays attached to the body without ever quite belonging to it.
Boil is not ordinary flicker. One plausible surface keeps replacing another. The image holds together long enough to be recognized, but not long enough to become continuous.
Its excess counterpart, Coatings, has the opposite trouble: one surface sticks to everything and will not come off.
Live self-portrait synthesized as Ryan Gosling in the manner of John Singer Sargent. The likeness holds, but the means of rendering it do not: brushwork, skin, hair, and background continually resolve and dissolve.