Even before the monsters begin their attack, there's a bit of horror in what happened to Merwin. He ends up hanging from what looks like either parachute wire or barbed wire, with him covered in blood.
The first sightings of what appears to be real monsters. Nick catches a glimpse of one while walking through the tunnel, and while they're trying to treat Merwin, Clarice is dragged into the darkness by one. And as the others wonder what happened, the monsters begin to scream as the survivors try and get away. Regardless of the truth, it seems like real monsters are here...and hungry.
After the rope breaks, Rachel survives her fall into the chasm by landing in a massive lake of blood and viscera. It makes one wonder how the vampires were able to kill and larder so many fresh bodies in an isolated part of the mountains. And then one starts following Rachel under the surface...
The vampires didn't fill the pit. Remember the Iraqi shepherds encountered early in the game? They're cultists who worship the vampires, and routinely throw travelers down to avoid being hunted themselves. That pit is a sacrificial larder maintained by unturned human beings.
Late into the game, when Salim and Jason make their way into the sprawling, inhuman underground caverns inhabited by the vampires, they find what they initially identify as the corpse of either Balathu or Kurum, determined by which character died first in the prologue. However, upon closer investigation, they see that not only is the corpse merely partially skeletonized, but through some horrible fate brought upon him by the vampires, the man is still alive despite half of his body having decayed. With Kurum and Balathu's segments being set in 2231 BC, that means that whoever they find has been paralyzed hundreds of feet below the earth in an inhuman cavern for over 4000 years, Salim naturally decides to take the poor sod out of his misery, putting to rest a life that has been conscious since the Akkadian Empire. What's worse is that the scientists that investigated the temple in the 40s identified that the creatures feed on fear and acquire adrenaline through fear they inflict, so it's likely that the vampires were keeping Balathu/Kurum alive for 4 millennia to subsist on his sheer horror.
Clarice's transformation. Her skin takes on an awful pallor, she makes almost inhuman screams, and you can see her skin stretch to accommodate vampiric height.
Rachel's fate in the "Lost in Time" ending. Being placed in a stasis cocoon to avert her transformation is the only way to save her life if Eric isn't both alive and aware of the vampires' weakness to UV light. If no one else survives to share that she's been left behind, though, she'll remain trapped down there for millennia. Given that the only other human we see coated in the stasis fluid is still conscious over 4,000 years later, this is probably a worse outcome than if the game ended with no survivors.
