The trick depends on a special microphone that Disney Research engineers invented. Named Ishin-Den-Shin for the Japanese term for "tacit understanding," the microphone records sounds and then renders them into a high-voltage, low-current, inaudible signal. The only way to hear the sound is to have someone hold the microphone and touch his or her finger to your ear. The sound is also able to move through more than one body, so if Alice is holding the microphone, Bobby can touch Alice's shoulder and Christy's ear to transmit the message to Christy. You can watch the Ishin-Den-Shin at work in a video from Disney Research.