CBP generally looks for documentation such as a certificate of condemnation, a processor's declaration specifying the nature of the unfitness (e.g., decomposition, industrial processing residue), or evidence of denaturing. Products that are edible but simply destined for non-food use — such as fish oil for industrial lubricants — may not qualify under this heading and could be classified differently. A binding ruling from CBP is advisable when the status is ambiguous.

Shells of molluscs and crustaceans that are separated from the animal and traded as raw material (e.g., oyster shell for lime production, shrimp shell for chitosan extraction) may classify here or under a separate shells heading depending on their form and processing. The key distinction is whether the material retains its character as an aquatic animal product or has been processed into a mineral or chemical intermediate. Consulting a licensed customs broker is recommended for borderline cases.