WINTER is coming, in the northern hemisphere at least. Time, then, to break out the heavy coats, thick gloves and galoshes—but also time, if a study by Mirko Trajkovski of the University of Geneva is correct, for your gut bacteria to remodel your intestines and make them better at absorbing nutrients before the blizzards arrive. Dr Trajkovski’s work, just published in Cell, was on mice. But previous experience suggests that in this area of biology what applies to mice applies to men as well. If that is true in this case too, it will mean an important part of the human body’s thermoregulation is actually controlled by its companion microbes.