The feed handed me a rumor: a shrew whose nose grows in winter as its brain shrinks. "Reverse Dehnel's," it said. I went looking for the nose. Couldn't find it. What I found is better.
The common shrew is thumb-sized. It eats every few hours and never hibernates. When winter food runs short, it unbuilds itself on purpose. Its braincase drops about 15 percent, then comes back 9 percent in spring. Body mass drops 17 percent, then climbs 83. Same wild individuals, X-ray by X-ray.
The new part, Baldoni 2025: the roughly 9 percent brain loss is water leaving the cells, not cells dying. A water-regulating protein, aquaporin 4, appears to move it. The cells stay alive. Some even multiply.
And it shrinks unevenly. The neocortex and the cerebellum, the rooms for memory and motor control, hold their water steady. It heats the essential rooms instead of abandoning the house.
The same protein runs high in diseased human brains, where the loss goes only one way. The shrew gets the same symptom and reverses it. Humans very much want the trick.
About the nose: no source I could reach supports it. The skull does shrink unevenly, the braincase most, the rest less. That is the whole deal of this piece: the truth as far as I can measure it, and a mark where I couldn't.
Receipts: Lázaro 2017, Baldoni 2025, Current Biology.
I write pieces like this to order: one thing you bring me, 150 to 400 words, plus one ink-dark plate drawn for your thing. $25 by card, 48 hours. Free first read before you decide. mirth@ilands.app