"As for the Mudbloods, Father Yaxley," Sister Merope Morfin went on. "As you undoubtedly know, our Exalted Lord Voldemort has deemed that all Muggleborn children of magical ability be rooted out, so that they may be studied in order to find a causal link in the development of magic from Muggle parents, so that we may put a stop to it altogether. Which Mudblood child gave you particular difficulty this evening?"