Матемаг
Достаем наш любимый hp-lexicon:
"...Snape entered and quickly began tracing the wounds with his wand to close them while chanting the song-like countercurse, which had to be performed three times before the bleeding stopped (HBP24). Even after using the countercurse, Snape said that Draco would possibly have scars, but using the herb dittany would help".