We all know what it’s like to have a commercial stuck in our heads, but what if they were quite literally in our heads? Public transit commuters might soon know what that feels like. A well-known advertising firm in Germany is working with “bone conduction” technology, which has already been in use by the deaf and by the military, but never before in advertising. A transmitter is placed on the window of a metro car and sends high frequency vibrations into the window. These vibrations are inaudible unless you happen to be a passenger who fancies a quick nap with your head against the window, in which case your head will act as a conductor and translate the vibrations into sound. You will actually hear the commercial inside your head. This gives a whole new meaning to getting stuck inside someone’s head.