Visible crew/equipment: When the plan to kill the lion is set with the old hospital, as they do a shot of the outside of the hospital, you can see what appears to be a crew member coming out of the tent in the front of the shot. (01:03:35)
Factual error: The actual Tsavo lions responsible for the killings had no manes - see for yourself; they are on display at the Field Museum in Chicago. [The filmmakers employed artistic license in using maned lions. They were also certain to include - at the very end of the movie - footage of the real Tsavo man eaters, as they appear in the Field Museum.]
Continuity mistake: In the scene where the lion is trying to get into the tree where Val Kilmer's hiding, it flashes to the lion, then Pitt, then the lion again. On the first lion flash its face is clean, then on the second lion flash its face is covered in blood.
Continuity mistake: After they find Remington's remains in the field, Patterson turns and begins to walk away. As he does so, he lower his rifle. In the next shot, he's holding it up again.
Chosen answer: The darker one is darkness, the lighter one is ghost.