"We just thought the winter was worse'n usual. Turns out we had an unexpected visitor. Wasn't until poor Dave and Glenda... died... that we finally got a clue. By then it was almost too late. You know how many of us'll never be the same? Oh, you doubt me, do you? Look in my eye, son, and tell me what you don't see. Yeah, I thought so. Damned Snow Devil!"
All you need to stop a brain is a bullet.
The Californian Sea Otter, as a species, eats about 30 different types of food found throughout its range. Each individual otter, however, will only eat 3 or 4 of these foods - those it was fed by its mother as a child. It will not eat the others even if failure to do so means it would starve. Maybe other, possibly larger and more dangerous creatures and monsters, have similar habits.