Adaptation Displacement: There is not only a book (The Man-Eaters of Tsavo, written by the real John Henry Patterson) but an earlier film based on it (Bwana Devil, 1952).
Awesome Music: Jerry Goldsmith was behind the film's score, giving us musical moments of adventure and dread, particularly the music used in the film's climax.
Nightmare Fuel: 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. 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.
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. At starts off happily, then Mood Whiplash kicks in.
At one point, fire reflects in one of the lion's eyes, as if hell itself was inside of them.