Here's a video clip, by Davide Laneri, of one e-puck sounding a tone on its loudspeaker, and the other hearing the tone and turning toward it. In order to make this work we've had to (1) turn the loudspeaker of the e-puck on the right so that it's facing directly forward (like a mouth) and (2) add 'ears' to the e-puck so that it has directional hearing. We've not done extensive tests because we've now decided to focus our effort, here in Bristol, on imitation of movement instead of sound.