Doubling as a Tear Jerker, the Lorax and the forest animals setting a circle of stones around a chopped tree. Something we wouldn't have though twice about otherwise was made raw and emotional through how it was handled. The Lorax couldn't have looked more sad had that tree been a dead forest animal.
Somewhat reversed in the end, with the people of Thneedville putting a similar ring of stones around the sprouting seed.
For Ted's third visit, he gives the Once-ler a bag of marshmallows. That small gesture indicates Ted's concern for the Once-ler and shows he cares about him, which means a lot to a lonely hermit like Once-ler.
Don't forget the cute little happy noise the Once-ler makes when he sees the bag of marshmallows.
The final musical number.
Seeing the art style transform into Dr. Seuss's during the end credits.
During the waterfall scene, after the Lorax saves Pipsqueak and young!Once-ler by rolling a boulder onto the bed, they're both launched off and, as they go flying through the air, Once-ler catches Pipsqueak, pulling him to his chest to break his fall.
During the last music number 'Let It Grow', the Once-ler chops down the wooden planks shutting his window closed, and hears the town of Thneedville on the horizon, finally agreeing to plant trees. Cut to the first time the audience sees the Old Man Once-ler's face, and he is tearing up and smiling! "Thanks, Ted."
Also, when the Lorax's final line to the Once-ler, which is all the more heartwarming considering his “Well Done Son” Guy issues.