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What is the tone of this passage by Jack London, about a dog being transported in a cage on a train?

The Call of the Wild

There he lay for the rest of the weary night, nursing his anger and wounded pride. He could not understand what it all meant. What did these strange men want with him? Why were they keeping him caged in this narrow crate? He did not know why, but he felt weighed down by the uneasy sense that some disaster was about to happen.