The stone-tool cut on the Castlepook reindeer femur is compelling because it sits between two interpretations: a brief episode of human carcass processing and a wider pattern of Upper Palaeolithic movement. The article stresses that a single marked bone cannot establish settlement, culture or occupation within mixed cave deposits and changing glacial conditions. Derryvree’s evidence of freshwater niches makes transient access plausible, while leaving routes and timing uncertain. What combination of dating, microscopic use-mark analysis, sediment reconstruction or comparison with neighbouring regions would most convincingly clarify whether this femur records an isolated visit or recurring human passage through Pleistocene Ireland?