What might explain the absence of gunshot residues on a subject?

The absence of gunshot residues on a subject can be effectively explained by the scenario where excessive blood is present. The presence of blood could obscure or wash away gunshot residue particles on the skin or clothing, making it difficult to detect them during forensic analysis. Gunshot residues are usually collected through swabbing or similar techniques, but if significant blood is present, it can interfere with the sampling method and potentially eliminate the ability to identify residues accurately.

While the other options may seem plausible in different contexts, they do not directly account for the physical presence and effects of blood in a way that could prevent the discovery of residue. Therefore, the scenario involving excessive blood provides a compelling explanation for why gunshot residues might be absent, emphasizing the importance of considering environmental and physical factors when analyzing crime scenes.