Pishachas love Mysticeti's blood so much that just the smell of it sends them into a frenzy. That's why Rak soaked some shutgun cartridges with blood, which impregnates enemies when he shoot them. The surprise came when Rak, testing the weapon, smelled the impregnated blood and went into the same frenzy as his pishachas. Try Rak's new weapon now!
https://www.youtube.com/watch?v=e2TH0Q5MMPA