Bullying
Explored primarily through Chad's treatment of Marshall, bullying is a major theme in Fuzzy Mud. Sachar subtly introduces the theme at the end of the first chapter: Cutting away from Tamaya socializing with her friends over lunch, the narrator's focus lands on Marshall across the lunchroom, where he sits silent and alone. This image is the first hint Sachar gives the reader that Marshall is disturbed by the bullying to which he has been subject since Chad joined the school. The narrator addresses the theme more directly in the third chapter with an extended commentary on Marshall's misery and confusion. For no reason he can discern, Marshall has become Chad's target. As a result, other students follow Chad's example and pick on Marshall as well, reducing him to a social pariah who resents having to attend school and whose grades are slipping. Sachar builds on the theme with Marshall's unkind treatment of Tamaya: Although Marshall recognizes she is the only student who isn't mean to him, he cannot help but snap at her during their walks to and from school. Ultimately, Sachar shows how bullying can plunge people into a defensive psychological state in which it feels as though they can trust no one.
Hubris
Hubris—excessive self-confidence or pride—is another important theme in Fuzzy Mud. Sachar explores the theme most directly through Jonathan Fitzman, the eccentric creator of Biolene. From the first excerpts of his testimony to the U.S. Senate, the reader understands Fitzman is too excited by his discovery of an environmentally friendly alternative to gasoline to slow down and consider the consequences of his experimental science. He reappears before Congress several years later with a much more subdued energy. After seeing the "ergies" mutate into the disease-causing fuzzy mud, Fitzman realizes he didn't factor in the potential of an oxygen-resistant form of Biolene escaping his laboratory and affecting the human population. Having seen the error of his ways, Fitzman apologizes for the unintended consequence of his invention—even as his lawyer insists SunRay Farms will not take responsibility for the rash epidemic.
Virtue
Virtue is another key theme in the novel. As a pupil at Woodridge Academy, Tamaya is proud to wear a sweater displaying the school's motto, Virtue and Valor. Meaning high moral standards and a commitment to acting for good, virtue is a principle to which Tamaya tries to adhere. While her friends engage in teasing and fibbing, Tamaya stays true to her sense of right and wrong. Her unwillingness to break rules makes her the subject of ridicule in the lunchroom, with Hope calling her a Goody Two-Shoes after she reminds the others that they aren't allowed into the forest beyond the school grounds. Tamaya also shows her virtuousness when she attempts to hide her rash from her mother, knowing that to tell her would risk getting Marshall in trouble. Tamaya also abides by her high moral standards when she risks her own safety to rescue Chad from the woods. Believing she can retrieve him without implicating Marshall, Tamaya sets out on her own, trying to do good without causing harm to others.
The Climate Crisis
Although less directly tied to the novel's main characters, the climate crisis—particularly the need to address it—is a major theme in Fuzzy Mud. Sachar establishes the theme as a presence that lingers in the background of the book but nonetheless influences events. If it weren't for the need to support a rapidly growing population on a warming planet, Fitzman wouldn't have received half a million dollars in funding for his sustainable alternative fuel source, Biolene. The need to address the climate crisis sooner rather than later also motivates Fitzman to move forward with his invention without considering the potentially catastrophic effects of mutant "ergies." Sachar returns to the theme in the novel's epilogue with a narrative commentary about how the Senate approves the continued development of Biolene despite its potentially hazardous properties. When weighing the threat of the planet heating up to the point of uninhabitability against the risk of another pandemic, the law-makers decide it would be far more catastrophic for them to set humanity on a course toward certain extinction, and thus decide to run the risk of continuing to fund Biolene.
Isolation
Explored through the behaviors of Marshall and Chad, isolation is another important theme in the novel. The theme first arises when Sachar describes Marshall sitting alone with his lunch while surrounded by students who are interacting with each other. The cause of his isolation turns out to be bullying. Unable to trust the people around him to be kind, Marshall retreats into himself, trying to suppress the painful emotions that come with constant social rejection. While Chad appears to have the opposite experience, enjoying plenty of admiration and influence, Sachar reveals that Chad is also emotionally isolated. To get away from peers he feels pressured to perform for and a family who mistreats him, Chad climbs ever-higher trees in the woods. Alone above the canopy, he can reflect on things and not worry about what others think.
Courage
Courage is a major theme in Fuzzy Mud. Meaning both the ability to do something despite being afraid, and strength when faced with grief or pain, the word courage comes from the Latin for "heart" (cor), the seat of emotions. Sachar introduces the theme with the narrator's commentary on the school's motto, Virtue and Valor. As a Woodridge Academy student, Tamaya hopes to meet the challenge of embodying these words by possessing both high moral standards and great courage. Tamaya shows the courage in her heart when she overcomes her fear of breaking the rules by following Marshall into the woods—an action she has to gird herself for by remembering a teacher's advice to pretend to be brave. Tamaya later shows genuine courage when she goes back into the forest to rescue Chad. By the end of the novel, Tamaya learns that without her selfless mission to save Chad, the world would have been gripped by a ruthless pandemic.
Infectious Disease
Though it doesn't enter the narrative until the last chapters of the book, the risk posed by infectious diseases is a major theme in Fuzzy Mud. After Marshall, Tamaya, and Chad are rescued from the woods, the town of Heath Cliff is at the center of the world's attention with news of the infectious rash created by the fuzz-covered mud Tamaya finds in the forest. As the rash rapidly spreads through the local population, the town enters a quarantine period in which no one may leave the area. This is done to limit the potential for other areas of the world to become infected. At the end of the book, Tamaya learns that her early encounter with the mud meant it was detected by the Centers for Disease Control and Prevention early enough that the rash didn't explode into a pandemic. Without her, the infectious disease would have spread to areas where the mutated ergonyms could thrive, safe from the freezing temperatures needed to kill the fast-replicating cells.
