Another motivation of the Blank Stare is to buy time to try to think up an excuse that is not actually a lie. Now she has to repeat the question she originally asked. The hapless man has just bought an extra thirty seconds. It won't work, of course, it never does. Whatever tactic employed, it only delays the pain.
Women are smart.
Men need to own up to that little fact. If we were smart, we would just tell the truth and take our punishment. Or if we were devious, we would just lie and then take our punishment because the female always knows when the male is lying. You see, the Blank Stare is actually the highest form of caring for the female. It is a sign of the latent goodness and honorableness of the man.