After thyroid surgery, a patient develops tingling fingers and hand spasms. The parathyroids (behind the thyroid) were bruised — PTH fell, blood calcium dropped. Low calcium makes nerves hyperexcitable: tingling around the mouth, carpal spasm when a BP cuff inflates (Trousseau sign), facial twitch on tapping the cheek (Chvostek sign). IV calcium gluconate corrects it acutely; the lesson is anatomical — the parathyroids' location puts them at risk in every thyroid operation.