What does Scout mean when she says, “By some voo-doo system Cal already seemed to know all about it?” (p. 103)

In chapter 11, Scout and Jem are walking past Mrs. Dubose's home on their way to the store when Mrs. Dubose begins to make derogatory comments toward them. Mrs. Dubose tells the children,

Your father’s no better than the niggers and trash he works for! (Lee, 105).

Jem becomes infuriated after hearing Mrs. Dubose insult his father and ends up destroying her camellia bush on their walk back from the store. When the children arrive home, they sulk in the kitchen until Calpurnia kicks them out. Scout mentions,

By some voo-doo system Calpurnia seemed to know all about it (Lee, 106).

Scout is humorously acknowledging Calpurnia's instincts and awareness that Jem has done something wrong. Calpurnia can sense that Jem has done something that will get him into trouble judging by his body language, depressed mood, and the fact that he is not excited about seeing Atticus when he comes home from work. Scout's inability to understand Calpurnia's innate senses and awareness is the reason she ascribes Cal's knowledge of Jem's offense to "some voo-doo system." From Scout's naive, childhood perspective, Calpurnia could only know about Jem's offense through some sort of magical, supernatural ability.