The Incredibowl m420 (aka the mini)

The Incredibowl i420 (the original)

You create suction, and light your smoking material in the glass bowl, drawing the smoke into the brass Smoke-Injection Nozzle.

The Nozzle acts as aheat sink while the hot smoke pools inside it, then the cooled smoke passes across the even cooler fine-mesh stainless-steel screen. Unlike pieces with metal screens near the heat, the tars in the smoke are cooled and have condensed by the time they pass through the screen, making them thicker, stickier, and easier for the screen to catch. The cooled, filtered smoke expands into the Expansion Chamber. When gasses expand, they increase in volume, decrease in density, and lose energy in the form of heat in the process. Other pieces leave much of this cooling, filtering, and expansion to occur in your throat and lungs, resulting in harshness and lost flavor.

When you create suction, you're creating a difference in pressure between the Expansion Chamber and the atmosphere outside the chamber (which your suction doesn't affect). When you pull the carb, the pressure inside the chamber has to become equal to the pressure outside, which forces air through the carb holes. The geometric arrangement of the holes causes the air to rush into the chamber as a symmetrical system of air jets that displaces the smoke quickly and smoothly into your lungs.

Other pipes and steamrollers let the air coming through the carb mix with the smoke because of turbulence, actually increasing the amount you have to inhale, and still make you create suction to inhale the mixture. Waterpipes make your lungs work even harder, because the water acts as a pressure lock that prevents the carb air from flowing any more than can fit in each bubble. The Incredibowl's carb uses the suction you've already created to blast large or small volumes of cooled, filtered, flavorful smoke into your lungs.