It was not a promise he could make, and they both knew. No matter how cautious, accidents could happen, from miscalculation or mistake. Fred and George had been careful, had pulled back and tried to neutralise the danger of their experimental potion. But they had used the wrong ingredients. It could happen to him as well but ... but he would do his best to avoid catastrophes if it left Harry that unsettled. One could heal from anything ... except death.