Fellrunner Failure?

I recently attempted to imbue a fellrunner with wisp essence and observed a rather curious reaction. Within a few seconds of the applied reagent, the creature simply dropped dead. Nothing out of the ordinary you might think, but upon closer observation the bird's carcass was gently steaming and the air was filled with a surprisingly mouthwatering aroma. Dissection revealed that the bird had been cooked from within, to perfection I might add. Conservator Vinelore seemed unimpressed by these results, but I want to attempt to recreate them in more easily available fauna.