Beakman gets "flushed" and 2 weeks later comes back to explan what happens to sewage after it's flushed. They use a demo to explain all of the steps of the sewage treament process including the names at each phase and what's happening at each step.
The Lorax confronts the Once-Ler, who has been cutting down Truffula trees to manufacture Thneeds. The two witness the cutting down of the last Truffula tree, marking an end to the viability of the Once-Ler's business. The lack of trees also adversely affects the environment, as is evident by the coughing of the residents of ThneedVille and the migration of all the wildlife.
As the main characters escape, falling off the cliff, they witness the bug-like creature that attacked them fall after. As the bug and excess rocks follow the main characters into the river, the effect of the weight creates a ripple, causing a tidal wave.