The weird step in the bore of the Denmark 1976 horn is covered by the hand so you can't be certain that it won't produce a sound. But it is certainly being play

The weird step in the bore of the Denmark 1976 horn is covered by the hand so you can't be certain that it won't produce a sound. But it is certainly being played wrong. Brass instruments are pressed against the lips, not placed into the mouth. The vibration of the lips is the origin of the sound.