Of the two boys, Tom Sawyer is much more devious; he acts as a foil to Huck in his brashness with Sally and he is cruel in his perception of Jim and desire to exploit the slave. Unlike Huck, who has observed Jim and interacted closely with the man, Tom has not learned to perceive slaves as fully human. Instead, Jim is merely "a nigger," a being with whom he can have some fun with no regard whatsoever to the man's feelings.
In Chapter XXXV Tom, ironically, tells Huck that they must make Jim's escape more complicated for it to be fun. He complains that there is no watchman to drug, and all they have to do is lift the bed to release Jim's chained leg. He feels that sawing off Jim's leg to free him "would be better still." And, he elaborates on other methods of escape, all of which would make the affair more interesting such as procuring a pen for Jim to make marks on his shirt as a log of the days he has been held captive. All of Tom's ideas indicate his attitude that Jim is worth no more than the pen or the ladder; he is just something in the game of escape that he plans.