Why did the men laugh at Buck when they brought him onto the deck at the end of the boat journey?

Buck experienced snow for the first time.

He sprang back with a snort. More of this white stuff was falling through the air. He shook himself, but more of it fell upon him. He sniffed it curiously, then licked some up on his tongue. It bit like fire, and the next instant was gone. This puzzled him. He tried it again, with the same results. The onlookers laughed uproariously...