No wonder Radagast lives here; just breathe the air for a free acid trip!
The Book: Thorin's Company walk the path, single-file. The forest was filled with massive cobwebs (though none spanning the path), black squirrels, and strange noises all around. The woods become incredibly dark; at night, it is completely pitch black, like it was in the goblin's caves. All of the dwarves, and Bilbo, hate the stillness and stuffiness of the air. During the nights, they could see glowing eyes in the dark, of various sizes and colors. Their rations begin to grow low, implying that the journey through Mirkwood took at least two weeks. The path is blocked by a river one day; heeding Beorn's warning, they do not drink from it or refill the water skins.
Bilbo, his eyes the sharpest, makes out an abandoned boat on the other side of the river. Fili throws a hook tied to a rope, guided by where Bilbo tells him the boat is, and on the third try he catches the hook to the boat and pulls it to their side of the river. Thorin decides that they will cross in groups of four: Dwalin and Bombur go last, because Bombur is so fat he needs to be on the lightest load. After all the dwarves had safely crossed the river, as Bombur was getting out of the boat, a great deer charges the dwarves and leaps across the river. Bombur gets knocked into the water.
Every group of friends has a Bombur.
The dwarves pull Bombur out, and he is fast asleep. Thorin's Company is forced to carry him for several days, even after they run out of food. When he finally does awake, he has forgotten everything since Bilbo's house. Thorin's Company does not lose the path through any of this. They hear eerie singing and laughing in the woods, which disquiets Thorin enough to order Bilbo to climb a tree so they could find out how much longer they must endure the forest. The hobbit does so. He basks in the sunlight and watches hundreds of black butterflies flying around his face. However, he is not comforted by what he sees - he sees no end to the woods in any direction.
My Opinion: I am very disappointed by how Peter Jackson handled Mirkwood. I was looking forward to seeing the enchanted river, but apparently that part of the book had to be cut for time. I guess to make room for exciting elven love triangles, I don't know. That's a big part of the chapter, though. Similar to the caves where Bilbo met Gollum, there seems to be an odd source of light present. Mirkwood is supposed to be dark and terrifying. Everything is just too saturated in orange and blue to really be menacing.
These butterflies are black in the book, but to be fair, I think Peter Jackson suffers withdrawal if his movie goes more than ten minutes without filling the screen with orange and blue.
At one point in the movie, Dwalin mumbles that he "doesn't even know what day it is." I can't tell if this is meant to imply that several days have passed, or just his general state of confusion. The movies certainly doesn't imply that more than a few hours had passed. That's something I feel the movie has gotten very wrong. The passage through Mirkwood feels far more sinister and epic if it's something that takes almost a month of travel. You shouldn't be able to get through it in a hearty afternoon.