Technical description of the workings of the bong:

First, the cannabis is loaded into the bowl, which you may remember was that thing sticking out of the bong. Do not ever tip the bong at such an angle that water can escape through the bowl. Anyhow, it is then burnt, and the operator commences inhalation at the other end of the device. This creates a vacuum within the chamber, and Nature, abhorring vacuums, pulls up on the water level, which increases the total volume below the water level, so the extra space, due to the same law of physics, is filled with the easiest-to-get available substance, namely air. This air comes from outside the bowl, which is ignited by the lighter and then converted to smoke as the cannabis is incinerated. This smoke is pulled into the water, forming bubbles of smoke. One of the advantages of the bong is that here, the bubbles supposedly shed many undesirable chemicals in the smoke, but not THC since it is not water-soluble. Anyhow, these bubbles, being less dense than water, rise to the surface of the water and eject their smoke into the vacuum of the chamber. This smoke is forced upward by the inhalation and then enters the respiratory system of the bong operator, creating a mild sense of euphoria.