The material escapes the label.
On this genus
A simple procedure makes something that needs another language to describe it. Gradients become terrain, cells become traffic, local rules become living tissue. Nothing unexplained has happened. The procedure completely determines the result, but its terms no longer describe what we see very well.
The second description is not just resemblance. Calling Rule 184 "traffic," for example, helps explain how it behaves. Some specimens escape as images, others as behaviors. Feral begins when one system becomes useful for describing another.
Feral is also the taxonomy's negative control. These specimens can look like slop without being made from an archive of prior images. Their complexity is procedural abundance without the archive: form from a compact process rather than accumulated cultural material. If they can show some of slop's symptoms without its cause, then unruly machine-made complexity is not enough to define slop.
Feral is not a drawer for awkward examples. It is where the theory keeps what it cannot quite digest. These specimens have escaped more than their labels — they have escaped ours.
A self-organising cellular automaton: procedural, with no training corpus behind it. Nothing here has been recognized as anything else; local rules generate the form from within. It resembles slop while lacking one of slop's suspected causes. Kept here because the boundary cases matter.