The lions. God, where could one possibly begin? Throughout the entirety of the movie, the lions lurk in the tall grass just out of sight. At times, one can see a tail swish from above the grass, but aside from that they are nearly invisible until they drop their stalking modes and attack. They seem to be almost supernaturally cunning and stealthy, and they're big (the first lion was measured at nine feet long). What makes all of this worse is that the film implies that they are not simply killing the workers for food, but for pleasure. Worst of all is that the lions portrayed in the film actually existed (sans manes) and many of the film's nightmarish events actually happened. What truly seals the horror is that it doesn't matter what the final total of kills was—it's estimated anywhere from 30 to 100, but historians have said the number is more likely to be between 28 and 31 people with the rest having abandoned ship to stay alive—this actually happened. The thought that two lions can act so far out of bounds and just start absolutely annihilating a human population taps into one of the most primal fears everyone has. It's no wonder the people who were there literally thought the lions were demons instead of animals.
The lion's den is littered with the human skeletal remains.
There is also the hospital massacre sequence in which the lions invade the hospital tent and proceed to slaughter everyone inside. At several times during this sequence, the lions' eyes appear to glow demonically.
Patterson's nightmare in which one of the lions attacks his wife and baby and the build-up to it. It starts off happily, then Mood Whiplash kicks in.
And then he wakes up from this, finds Remington missing and rushes outside in a panic. We're then treated to an overhead shot of him and Samuel at a bloody patch of grass that has become Remington's final resting place. This one's a twofer plus one; first, it's proof that the lion was inside his tent as he lay sleeping and could have easily killed them all, so it's almost as if Patterson is being taunted. Second, Remington's death comes off as a Worf Effect as he had more hunting and combat experience and had served in the Civil War, on the Confederacy, no less. Finally, whatever was done to him was so gruesome that, in a movie which is not shy about displaying the lions' handiwork, his death had to be presented as a Gory Discretion Shot.
At one point, fire reflects in one of the lion's eyes, as if hell itself was inside of them.
Real Life example: Just hop over to the Trivia section and read the director's account about what he, the cast, and the crew went through just to make this film on location. Compared to that, the movie's events seem like a backyard campout.
The final lion makes it perfectly clear that the death of its kin turned it even more feral. And what's even scarier is the real life account. Allegedly, it took nine shots from a rifle to kill it, and the last shot was with Patterson up in a tree having to shoot it in the head at point blank range to kill it for good. His firsthand account also claims that even as the lion bled to death from its wounds, it was still gnawing on the tree branch trying to reach him. Once again, it's no wonder the people who survived this ordeal thought these lions were demons, not regular animals.
