Sid hears Tom saying,
"It's blood, it's blood, that's what it is!"
Sid says that Tom repeated these words over and over, and then he said,
"Don't torment me so - "I'll tell!"
Obviously, Sid is very curious about what it is that Tom has to tell.
Tom's troubled sleep is the result of a tormented conscience. He and Huckleberry Finn have inadvertently witnessed the murder of Dr. Robinson at the graveyard, and they know that the killer is Injun Joe. Injun Joe, however, has managed to convince Muff Potter, who was also present that night and was very drunk, that he (Muff) is the one who did the killing. When Muff Potter is arrested for the crime and confesses, Tom and Huck feel very guilty for not coming forward with what they know. In all fairness to Muff Potter, they know that they should, but they are afraid of Injun Joe.
Afraid that he might continue to talk in his sleep and reveal information which he would rather keep a secret, Tom pretends that he has a toothache and ties his jaw every night when he goes to bed so that he will not be able to speak in his sleep again. Craftily, Sid slips the bandage off of Tom while he is sleeping, and stays awake in hopes of learning more about what is on his brother's mind. Fortunately for Tom, his "distress of mind" gradually wears off, and Sid does not get any more information (Chapter 11).