Singing in Lake Toba, Sumatra, Indonesia

I was taking an evening stroll around the streets of Tuk Tuk, on the shores of Lake Toba, Sumatra, when I came upon a group of eight or ten men with guitars.  They were happily singing local songs and drinking local palm wine, called tuak, which is a thick opaque alcoholic beverage that smells like rotten eggs (to me, anyway).  They were so engaged in their singing, I don't know if they ever noticed me.