Evil, unsympathetic orc creatures begin eating another orc, which they just decapitated, all that is seen of the act itself is an intestine flying up in the air, it is easy to miss, however this is all still pretty disturbing
The main battle sequence also features scenes of women and children hiding within the fortress and crying.
Easily one of the darkest, most hopeless, and bleakest entries in the trilogy by a wide margin.
Armies of orcs are grotesque, with rough voices and yellow eyes and sharp teeth. A few of them have blood dripping out of their mouths. They are very frightening. The orcs are shown in several scenes.
In a scene in which the main character falls into a marsh that carries the souls of dead people, we see very scary, grotesque ghosts trying to pull him in before he is instead pulled out. This scene is disturbing and very scary.
The servants of Sauron are clad all in black with their faces invisible. They emit loud screams and talk with a very evil, low voice. They ride grotesque flying creatures that kill people and good guys without mercy, mostly by picking them up and letting them fall.
Gollum is a frightening, frightening creature, who is present through most of the film, though he talks and interacts with main characters.