London's writing is generally realistic, but he sometimes resorts to hyperbole in order to convey for the reader a more vivid scene. For example, in Chapter 6, London uses a hyperbole as he describes how Buck rescues Thornton from the river:
Buck held on till he was on a line straight above Thornton; then he turned, and with the speed of an express train headed down upon him.
Thornton has fallen off a raft, and he has gotten stuck in some rapids. Buck has attempted to pull him to shore, but Thornton's grasp on Buck's tail could not endure the force of the water. After Hans ties a rope to him to help pull him back to shore, Buck proceeds to dive back into the rapids multiple times until he finally manages to catch Thornton and pull him to shore.
In the quote above, London writes that Buck launches himself toward Thornton "with the speed of an express train." By 1903, when London published The Call of the Wild, the fastest trains could go around 130 miles per hour. This is significantly faster than Buck could possibly move, even during an adrenaline rush. London does not expect the reader to believe that Buck has actually developed supernatural speed and strength. Rather, the exaggeration adds action to the words on the page. By trying to imagine a dog moving "with the speed of an express train," the reader ends up lingering on Buck's body in motion, trying to speed it up in their mind's eye.
