The photo below is a Hohner Piano 26 to which I added a bead of silicone to the back to help seal the sound outlet against my chest. With this arrangement–particularly when used with a vinyl melodica apron–you can fully choke the outlet. When pressed against your chest, you get a soft smooth sound. As you allow one side of the melodica to lift from your chest, the sound become louder and brighter. Movement that ranges anywhere between holding the melodica super tight against your chest to waving it freely in space (and in and around the microphone) produces a wide range of tonalities and modulations.
This photo shows an early experiment. I normally cut off the standoffs, water valve outlet hood, and remove the handle before adding the silicone.
When I say hold the melodica at the bottom, I mean at the bottom where the water valve is. Obviously you can’t hold the melodica from the back side and press it against your chest.