Pretty cool. Inmates in the camps generally weren't allowed to conduct any sort of meetings or services for any reason. The guards didn't want them organizing a revolt. But they'd often find a way to do it anyway. The movie Paradise Road (which I recommend if you haven't seen it) shows women in a Japanese camp putting together a vocal orchestra. One woman wrote down an entire Beethoven symphony from memory and they'd practice the parts in twos and threes. Then one night they put it all together and performed. The guards went running towards them with their guns as they saw the women assembling, but stopped in their tracks once the women began singing.

Another story I have read was in Corrie Ten Boom's account of life in German-run camps. She and her sister would have prayer meetings in their bunkhouses. They couldn't understand why the guards never stopped them, until one day they learned it was because the bunkhouses were infested with fleas and the guards weren't willing to risk the fleas in order to break up the meetings.