While Tara is studying at college, she becomes ill and finally takes penicillin, which symbolizes her rejection of her family's values. By this point, Tara has been educated enough to understand that many of the rules her family imposed do not make sense in the modern world. She has grown up with the belief that taking medicine is bad for her, but she is tired of suffering needlessly, and wants to live like a modern woman. Taking the medicine is a significant symbol that Tara is moving away from the values she was taught while growing up. The moment is so significant that Tara reaches out to tell her mother what she has done. This choice also symbolizes Tara's increasing boldness, and her willingness to be honest about the woman she is becoming.
Caravaggio's painting symbolizes how Tara's education gradually progresses and how she becomes someone who is comfortable as an intellectual. She first sees the painting as an undergraduate in her art history class, at a time when she is struggling with her studies. With her limited experience, the violent painting—depicting a woman beheading a Syrian general—reminds Tara of someone killing a chicken. Later on, when she is a graduate student, Tara sees the painting in person while visiting Rome. By now, she has become much more educated and sophisticated, and she can appreciate the painting as a work of art. The difference between how Tara responds to the painting both times shows how far she has come, and how she has turned into someone with a much more nuanced view of the world; she can see beyond the life she lived in rural Idaho. In effect, the painting symbolizes the power of education to transform someone from being a very sheltered and limited individual to a thoughtful, cosmopolitan woman who can freely travel the world.
When Gene tells Tara's brother, Shawn, about Tara's allegations of abuse, Shawn comes to the house with a bloody knife, which symbolizes his violent rage. Tara is not sure whose blood is on the knife, and that uncertainty makes the gesture even more menacing. Shawn uses the knife as a way to assert his dominance and power, knowing it will scare Tara. He is successful in getting Tara to say that it was all a misunderstanding, and retract all her accusations. The knife symbolizes how even once Tara has spoken up and tried to stand up for herself, Shawn still wields all the power within the family dynamic. He will not back down, apologize, or try to change. He is furious that Tara dared to try and challenge him. No matter what, Shawn will always be a violent person who needs to be in control and assert his power over his younger sister.