Soulgaze

When a practicing wizard and a being with a soul (all mortals along with White Court Vampires and others) look each other in the eyes, it begins what is known as a Soulgaze. It gives the other a window into their soul, which can't be faked. It doesn't relay specific information (you can't use it to interrogate someone), but it does give one a vague impression on whether they're trustworthy or not, or if they've been psychically harmed, etc. Just like if one were to use their Sight, the memory of the gaze doesn't fade with time, being as sharp years later as when it happened. One circumstance in which a Soulgaze doesn't occur, is when a doctor looked into Harry's eyes. He didn't so much as look into his eyes, as examine them, which is professional intent.