I was worried that it might be a goat that gets harmed, but it's not: it's a short scene where a woman uses a vole for divination purposes, i.e. to read its entrails. It's very much a one-sentence background event (relevant though - the background in this fic is fantastic, it makes me think of a Rembrandt painting) and you should not let it put you off.

Then again, I've got a bit of a crush on Aberforth, I might be not entirely objective ;-)