What puzzled Buck when he stepped onto the deck of the Narwhal in Call of the Wild?
When Buck stepped onto the deck of the Narwhal, he stepped into "a white mushy something very like mud". He was puzzled, because it was the first time he had seen snow.
Buck had been raised in the "sun-kissed Santa Clara Valley" in California. After being stolen from the ranch which had been home to him for all his life, he was transported by train and then by boat to the northern state of Alaska. During his time on the Narwhal, Buck was kept between-decks with a number of other dogs, so he was not really aware of the full extent of the change in his environment.
"Day and night the ship throbbed to the tireless pulse of the propeller, and though one day was very like another, it was apparent to Buck that the weather was steadily growing colder. At last, one morning, the propeller was quiet, and...(he was) leashed...and brought...on deck".
Buck stepped onto the cold surface of the deck into a layer of snow, and in astonishment, he "sprang back with a snort". Snow was falling from the sky as well, and although he shook himself, it continued to coat his fur. Buck sniffed at the unfamiliar matter, and tried to lick it with his tongue. Onlookers laughed at his antics, his reaction to his first experience with snow (Chapter 1).