In act 1, scene 3, Giles Corey asks Reverend John Hale, "What signifies the readin' of strange books?" Corey goes on to explain that he often finds his wife, Martha, reading strange books, and while she is reading these books, he is unable to pray. Corey explains,

I tried and tried and could not say my prayers. And then she close her book and walks out of the house, and suddenly—mark this—I could pray again!

Giles Corey tells Hale that he is not trying to suggest that his wife "touched the Devil"; he says he just wants to know what she is reading and why she hides it from him.

Later in the play, Martha Corey is arrested and accused of being a witch. Once Martha is arrested, Giles regrets having talked about her reading habits and gets kicked out of the courtroom while trying to argue for her innocence. Eventually, Giles is also accused of witchcraft, and upon refusing to confess to it, he is pressed to death.

Giles Corey causes problems for his wife, Martha, when he states that she reads "strange books" in Arthur Miller's The Crucible. Giles asks Reverend Hale about the meaning of his wife reading strange books. He goes on state that he cannot pray when she reads, and he states that she hides the books from him. All of this places Martha in the middle of the accusations of witchcraft in Salem. Although Giles has no clue what his questions would lead to, Giles stating that his wife reads strange books leads directly to her being accused of witchcraft. Even with Francis Nurse and Giles Corey stating that Martha is close to God, she is still accused because of Giles' statements. 

What does Giles Corey accuse his wife of in The Crucible?

In act 1, Reverend Hale arrives in Salem and is considered an expert in anything involving supernatural forces, demons, spirits, and witchcraft. At Reverend Parris's home, Hale shows off his impressive collection of books regarding the "invisible world" and Giles Corey innocently brings up the fact that his wife, Martha, seems to be reading strange books. Giles Corey goes on to say that he has found his wife several times reading mysterious books at night and cannot identify the books because she hides them once he enters the room. Giles Corey also admits that he feels uncomfortable when he sees his wife reading and has difficulty praying while she reads. He goes on to mention that he does not think that she has "touched the Devil," but he is suspicious about the books that she has been reading. Unfortunately, Giles's minor concerns are exacerbated when Martha is arrested and accused of witchcraft. Following Martha's arrest, Giles Corey feels extremely guilty for even mentioning the fact that she read unfamiliar books and wishes he never said anything about it.

What does Giles Corey accuse his wife of in The Crucible?

He does not overtly accuse her of being a witch, but he does tell Mr. Hale that Martha has strange habits. For one thing, Giles can't understand why Martha enjoys reading. He tells Hale that the night before, he tried and tried to say his prayers but could get nothing out. When Martha closed her book and left the room, however, the prayers came easily to him. Without intending to, Giles Corey has given evidence to condemn his wife of witchcraft.