Oscar the Headmaster

We are currently having our loft converted and our house is crawling with builders, and some days the noise is deafening. Could somebody please explain to me how Oscar can manage to sleep through someone using an angle grinder to cut through a large steel girder about 12 feet from his cot, but always seems to wake up if I creep into his room at night to check on him? Or how when the plumber set off the fire alarm that he didn't even stir, but gets very upset if I sneeze, or open a packet of sandwiches too close to him?
Come to think of it, Oscar gets very indignant at the moment if I eat anything in front of him. He gives me his 'headmaster's look' - as if to say, "What are you chewing? Spit it out immediately or I'll put you in detention after school." He thoroughly enjoys his little pots of baby gloop, but I suspect my chocolate bar or roast dinner looks a lot more interesting. All in good time, little bean!