The mood of the novel shifts as Bilbo gets into and out of dangerous situations. Tolkien often uses imagery and other environmental details either to build a sense of dread and despair or to put the reader at ease. For example, in Chapter 7, the adventurers are intimidated by their environment as they arrive at Mirkwood:
The land began to slope up and up, and it seemed to the hobbit that a silence began to draw in upon them. Birds began to sing less. There were no more deer; not even rabbits were to be seen. By the afternoon they had reached the eaves of Mirkwood, and were resting almost beneath the great overhanging boughs of its outer trees. Their trunks were huge and gnarled, their branches twisted, their leaves were dark and long. Ivy grew on them and trailed along the ground.
Bilbo and the reader have perhaps never been so conscious of the sights and sounds that ought to be present in nature as when the birds go quiet and the deer and rabbits (prey animals) disappear. It seems that all these animals have either been killed or learned to stay away from this place. The darkness and "murk" ahead is itself ominous, especially given the way light is always saving Bilbo from peril in the dark. The "huge and gnarled" trees seem to make up an old-growth forest, allowed to grow wild over many centuries. In the middle ages and earlier, England was full of these impossibly thick forests that were felled for land development. The ancient forests became legends all their own and have often been associated with danger and magic. Furthermore, the ivy-covered, old-growth trees create a dark natural edifice with "eaves" that lean over the path where the adventurers are walking. This architectural term suggests that Bilbo and the dwarves may as well be walking into a dark, abandoned castle no longer fit for the living. When Tolkien sends his adventurers into Mirkwood, it is as though they are walking into a gothic fairy tale. Readers are filled with anticipation and fear for what might await them there and for who reigns over this terrifying place.
All of the doom that pervades this passage stands in stark contrast with earlier moments in the chapter, when the characters feast on delicious food and enjoy each other's companionship:
At last Gandalf pushed away his plate and jug—he had eaten two whole loaves (with masses of butter and honey and clotted cream) and drunk at least a quart of mead—and he took out his pipe. “[...B]less me! this is a splendid place for smoke rings!”
Bilbo gets frustrated with Gandalf for eating and smoking at length while avoiding his and the dwarves' questions, and the reader likely also gets frustrated waiting to find out more from the wizard about the mysterious Beorn. Still, the way Tolkien lingers over vivid descriptions of food and smoke rings gives the reader a sense of safety and luxury. There is time for Gandalf to draw out this moment and enjoy himself. These moments of safety (especially those surrounding food) interrupt moments of great danger and hardship throughout the novel. Cozy and often a little humorous, they give the characters and the reader a respite, as well as a chance to revel in the companionship that is strengthened every time the adventurers overcome an obstacle. Tolkien may instill readers with dread and despair sometimes, but he always follows these feelings up with reassurance that better times are ahead.