In To Kill a Mockingbird, when Mr. Ewell is asked if he is the father of Mayella, why does he respond in this manner, and what does it imply?
Mr. Ewell states, "Well, if I ain't I can't do nothing about it now, her ma's dead."
I think that, for the most part, Bob is trying to bring a bit of unsophisticated and disrespectful levity to the very serious matter of a rape trial. Bob's answer is meant to be funny although it is certainly no time for joking around with Tom's life on the line. Perhaps more importantly, his humor is an insult to his late wife; the statement seems to be questioning whether--joking or not--Bob is actually the father of Mayella. The implication is that Bob's wife may have been cheating on him, and that Mayella is not his biological daughter. Bob seems to be saying that if Mayella's mother was still alive, he could deal in some matter--probably physically--with the situation of her possible infidelity. His statement leaves this possibility open, though I tend to think it was just a crude joke on Bob's part.