What do you thinkobrien was referring to when he stated that winston already knew what was inside room 101

Everyone is terrified of room 101. Remember the skullface guy? Room 101 holds an unspeakable terror unique to each individual. Winston knew that whatever lies behind that door was his greatest fear and his alone. Winston was also aware that he hated rats the most. Winston always knew what was inside that room although he might not have consciously admitted it.