After inhaling the saline mist through the mouth it is possible to exhale through either the mouth back into the nebulizer cup, or through the nose avoiding the cup. My natural tendency is to inhale and exhale through the mouth and I have to really think about it to exhale through the nose (opposite airway clearance techniques). But I tried it and didn't seem to make a difference anyway. I know some people inhale through nebulizer then exhale through Aerobika, which might avoid foam in the cup. ??