This is especially useful when trying to extract information from people, allowing Sherlock to deduce key facts from the smallest of details. When questioning the boy about his father, for example, we had to decide whether the boy's eyes were watering because of an infection or because he was recently crying; whether a sewn-up tear in his clothes indicated his parents were caring; or whether the fact he carried a map of London means he's educated enough to read. Get these right and they cause the character to warm to you, potentially unlocking key information.