but there was also , when he woke up after half an hour ( he was a lousy sleeper ) , the slick tongue of guilt licking behind his ears in the quiet of the apartment , whose walls and windows were too thin to keep out the sounds of the working world , the mutter of traffic on market street slashed by hostile farting of motorcycles , the tapping of hammers at some local construction project , electronic piddling of telephones in surrounding apartments , all the little tinkerings of people with busy lives .