aplomb

“Oh, Wooster,” he said, “I was talking to my mother a night or two ago.” “Oh, yes?” I said, with a slight wave of the hand intended to indicate that if he liked to talk to his mother anywhere, all over the house, he had my approval. “She tells me you are interested in mice.” I didn't like the trend the conversation was taking, but I preserved my aplomb. “Why, yes, fairly interested.” “She says she found you trying to catch one in my bedroom!”