The tugging grew more insistent, bordering on becoming painful. Only now did Severus realised that he was being summoned. With Voldemort, there had never been any doubt. The Dark Mark's pull like fire in his veins, created to cause suffering, even madness, when a Death Eater resisted. While Harry's mark was not comfortable, it was far from unbearable. Though, just because it didn't hurt did not mean he could effort to ignore it.