The river behind our town freezes for about three weeks every January. When I was a child, everybody walked on it. My father says his grandfather once drove a cart across it, with a horse. Now the ice is thinner. Some years it does not form at all. Last winter it froze properly for the first time in six years. The whole town came out. Somebody brought a table and sold tea in the middle of the river, which felt illegal and probably was. An old man stood at the edge and refused to go on. "It is not the same ice," he said. People laughed at him, but he was right in a way nobody wanted to hear. He explained it to me later, sitting on the bank with his hands in his pockets. Ice that forms slowly, over many cold weeks, is thick and even. Ice that forms in four days, after a sudden freeze, has air inside it. It looks identical from above. "You cannot see the difference," he said. "You can only hear it." He told me to listen. There was a low sound under the noise of the crowd, a kind of deep complaint, moving from one side of the river to the other. Nothing happened that year. The ice held. But I go to the edge now and listen before I walk out, and I have not walked out since.