We wandered through wide hallways trimmed with metal pipes, ducked into bare-brick workspaces lit by industrial-scale anglepoise lamps. We met a man who had invented a new musical instrument and another who was building a better mouse. I almost said "Mousetrap?" but realised in time that he meant exactly what I thought he meant, although of what benefit an improved rodent could be I had no idea. He explained that the digestive systems of vultures are purgative of disease. The birds’ excreta are pure fertiliser, even the most revolting diseases burned out by their fierce internal chemistry—for which reason the killing of vultures across the world represents an unprecedented risk to global public health. In many areas where they are almost extinct, bad old germs are resurgent in their place. He wished to introduce the vulture’s happy trait into urban rodent populations, a giant leap towards the eradication of serious infections—and crucial in a world that is rapidly losing its grip on resistant bacteria.