Complex sentence: Warren and his assistants later expressed astonishment that Abigail endured the pain of the surgery and cauterization without crying out, despite the gruesomeness of the operation, which was so horrifying it caused her mother, husband, and daughter to turn away.
Split into simpler sentences: Warren and his assistants later expressed astonishment that Abigail endured the pain of the surgery and cauterization without crying out, despite these actions being so gruesome. They were so horrifying that they caused her mother, husband, and daughter to turn away.