Fulachtaí fia are burnt mounds, found in their thousands across the island, and typically understood as cooking sites where stones were heated in fire and dropped into a water-filled trough to bring it to the boil. The second of two such features found at Tullahedy, however, produced no trough at all.

Donald Murphy's excavation revealed a rectangular spread of burnt and heat-shattered stone measuring 41 metres by 21.5 metres, a substantial footprint by any measure. Beneath that spread, 30 small pits were recorded, but whatever function they served, none matched the trough that is usually considered the defining feature of a fulacht fia. The absence is significant. Debates around these monuments have long circled questions of function, with proposals ranging from communal cooking and food processing to textile dyeing, hide working, and even bathing. A site with the characteristic burnt material but without the expected trough fits awkwardly into any single interpretation, and that awkwardness is precisely what makes Tullahedy worth attention.