I work with severely emotionally disturbed children. You have to be able to hear their screams when they slam their wrists into plate glass windows, throw microwaved boiling water into each others faces, hit one another with baseball bats, beat dogs to death in the back yard, fuck the youngest boy in the bathroom, or make plans to rob a neighbors home… (actually, lip reading might be cool in some situations. But I have gotten real good at reading body language.) I know for a fact when someone is in posession of drugs. The entire energy changes. One person becomes the focus. Everyone starts talking to him in a friendly way. Something is up. Ears are just a big part of the job.