This is the flutter:
http://www.axcan.com/pdf/flutter.pdf
The patient breathes through the Flutter against resistance, which is generated by blowing a small stainless ball upward inside a cone at the of a pipe-shaped device. The ball covers the opening of the cone; as it vibrates within the cone, it keeps pressure in the bronchi high during expiration and thus the bronchi remain open. When breathing out against the pressure of the ball, it also produces low-frequency vibration impulses that ease the transport of the mucus secretions. So basically, you take a deep breath, blow into it slowly, and your lungs vibrate and lossen mucus.