Nightmare Fuel: The Big Bad. He eats people, and his own flesh is slowly dissolving away as he morphs into...something.
Fridge Logic: Getting the compass wrong wouldn't have made them walk in circles. Aiming for the same peak continually should have prevented that unless they somehow climbed down the same side they climbed up.
Tear Jerker: See Bittersweet Ending. Bob's death is pretty heartbreaking too - even if he tried to kill Charles, seeing him dying just before the rescue is quite painful.
The Un-Twist: After the bear is killed, just when the viewer thinks the narrative thrust of the film has been about Charles overcoming his distrust about his wife's possible infidelity, in a very Mamet twist it turns out that — surprise! — Bob was sleeping with her after all.