An example from speech of "man's inhumanity toward man": While Huck is pretending to be Tom Sawyer and explaining to Mrs. Phelps the reasons for his delay in arriving, he tells her that an accident delayed him but no one was hurt, except for an African American who died. Mrs. Phelps expresses relief that "no one" was harmed.
This is a clear lack of the application of the basic idea of humanity in regards to African Americans.
Tom Sawyer's behavior, from his plan to his big secret, presents a number of examples of the theme in question. Tom inflicts rather horrific rites on Jim so that Jim can escape. All the while, Tom is aware that Jim is already a free man.
An example of attitudes that express this theme can be found in the community's view of Jim after he attempts to escape. The people condemn him, treat him in ways that are blatantly unfeeling and espouse views of Jim that reduce him to something less than a man.
One example is clearly represented by the scandalous, base, and criminal acts of the "king" and "duke". They are both in a constant quest for self interest and self gain, without taking into account other people's losses.
We can see another example in Huck's father abusive treatment: he prohibits Huck to ever go back to school, he compels him to provide him with money, and he even kidnaps him, overlooking the law, and forces him to go live with him.
A third instance of inhumanity we can observe in the crowd's reaction when they find Jim. They want to kill him, publicly humiliating him so that he will serve as an example for other black people who want to run away. The crowd's attitude signals a readiness to judge people in a very hasty way, without hearing their defense first.
Another example is depicted in Tom Sawyer's thoughts about how Jim has to suffer like a real prisoner. Tom even considers the possibility of sawing Jim's leg off instead of just sawing off the bed's leg. Besides, Tom makes Jim's life more uncomfortable by bringing into the cabin spiders, rats and snakes. This shows a serious lack of sensibility in Tom towards other people's feelings.