Hands

If you have a good cup on the harmonica, you can move any digit and achieve a Wa Wa... give this a try. If you don't hear a difference in sound with just a little bit of movement, it means you have some leakage. Try cupping the harmonica, then dropping the harp in your lap... keeping your cup intact... and blow into your cup (hands against your face, just like when you play) and where air leaks out is where you'll need to seal more when you have the harp in your hand.