Vanesa Martín starts this one in the most ordinary way possible. She wasn't looking for anything: "No buscaba nada en especial" (I wasn't looking for anything in particular), just "Un par de vinos" (a couple of glasses of wine) and a laugh in some bar. Then her loneliness speaks up at the counter, and someone sits down beside her that neither of them saw coming. Outside it's raining again, windy and cold, and the meeting feels "Como bajar un río" (like going down a river): fast, and impossible to stop.
The chorus is where the title earns its keep. She asks "Cómo hacemos el amor sin que se note" (how do we make love without it showing) when "sabemos bien que nos haremos daño" (we know full well we'll hurt each other), because they are "dos erizos deslumbrados" (two dazzled hedgehogs) "Al filo de una carretera" (on the edge of a road). It's a great image: hedgehogs frozen in the headlights, and hedgehogs that can't get close without pricking each other. Listen for "Desactivando alarmas" (switching off alarms), her way of saying they let their guard down one touch at a time, and the half-joking line "La ambulancia va en camino" (the ambulance is on its way), as if this love were a crash scene.