[Understandable isn't justification. There are a lot of things that are understandable that aren't justified. But Law knows wild creatures - or at least he knows Bepo. He knows that wild animalistic urge to defend when backed into a corner, regardless of who's the aggressor or not.

So in this case...]

... aa... [There's subtle but visible relief in that sigh. Not the worst case scenario. No witch hunt to worry about. He'll have to look into the victims... but right now that can wait a while. The tone is asking for help and help he will give.] I can help with that, then. The Battle Dome has transfusion supplies and I believe Good Spirits still has a stock of blood for any vampires in town. I'll make sure to find out if that's still the case if a back up is needed.

[If not, he'll just hunt animals in the woods and bleed them if worst comes to worse. He can barter the meat and skins with the people receptive to a trade, perhaps get something useful in return.]