These hollows, known as cup-marks, are among the most enigmatic markings left by prehistoric communities across Ireland and Britain. Rarely more than a few centimetres across, each one was ground out by hand, and nobody has convincingly established what they meant to the people who made them. The Knocknageehy stone has thirty of them, distributed across both its east and west faces, which suggests the carver, or carvers, worked their way around the stone rather than treating only one surface as a canvas.

Cup-marks appear widely across the Irish prehistoric landscape, often on exposed outcrops or large boulders, and occasionally in association with megalithic tombs or stone circles. Their date is difficult to pin down precisely, but they are generally attributed to the Neolithic or Bronze Age periods. The Knocknageehy example is a recumbent boulder, meaning it lies flat rather than standing upright, and it is partially embedded in the soil, so some portion of the stone and potentially more markings may be obscured below ground level. The individual cups here reach a maximum diameter of seven centimetres, which is fairly typical for the form. The fact that the carvings appear on opposite faces of the same stone is an interesting detail, raising quiet questions about whether the stone was always in its current orientation or has shifted over millennia of agricultural activity in the surrounding field.