“Mm? What’s that, my boy?”
A trick often used by wily senior citizens when they need a second to gather their thoughts, or just to ignore the fooling thing someone has just said. The First Doctor never skimped on being brash or rude when he could help it, so possibly he really was a little hard of hearing, or slow to work out what to do. Either way, his need to slow a conversation down, or obfuscate an awkward line of inquiry, stood him in good stead, and served to reinforce the misleading idea that he was just a doddering old gipper, before he delivered the coup de grace.
via BBC America
