The British are a nation of rubberneckers: we chase ambulances as though they’re ice-cream vans, and our paramedics play to packed houses. But here, on the US-Mexico border, a curious nature will get you more than a close-up. Gawpers are in short supply where blue lights spell danger. At the first sound of a siren, people scatter or turn their backs – it’s better to face the wall, lest, seeing something you shouldn’t, you wind up sliding down it.