Aglais io, or the European Peacock, is a striking but reasonably common butterfly found in Europe and Asia.
The eye spots on the butterfly’s wings are to deter avian predators, which is all well and good when it’s outdoors in the summer. During the winter, though, when the butterfly is hibernating in the dark, they aren’t much use at all against mice and other rodents. In these cases, it will hiss.
I had no idea that butterflies could make such a noise.