The etiquette, presumably, was simply not to kill each other point-blank. At the very least, that seemed to be what Draco was going with.

"Looking around at what?" He asked then, a frown furrowing his brow. Despite the cold, he was managing to stay warm enough, and so he approached further, joining her near the edge of the crevasse - peering in briefly with mild concern - and then dropping himself to sit beside her, harpoon at the ready to his other side. "There's not much, besides the snow."