Why were the Judge, Papa, and Billy laughing?

The Judge, Papa, and Billy were all laughing at Grandpa standing in front of the fire trying to dry his clothes..... which were steaming.

After killing the coon, we built a large fire so Grandpa could dry his clothes. He’d get up as close to the fire as he could, and turn this way and that. He looked so funny standing there with his long underwear steaming. I started rolling with laughter. He looked over at me and snapped, “What’s so funny?” I said, “Nothing.” “Well, why are you laughing?” he said. At this remark, Papa and the judge laughed until their eyes watered.