Rattlesnakes

It happened right here, at the end of that broad tunnel.
It was back when I worked as a Constable, though I wasn't tracking a lost but a client who has been looking for the right thing in the wrong places, as we all do from time to time.
I had my tester, my Beat, a latern and Lazuli, but I was still worried. I had heard what happens to people who enters certain caves. Most of the caves.
Some may say that, for what you should feel here, I wasn't as scared as I could have. And sure, there was the company's time loop. But I was at least wary.
I let the [ancient light] go first, of course, and walked through tunnels as clear as the day. Yet I didn't see them. I heard the bells, but I didn't know what they meant. The few months I had been working with The Company had already taught me that even those cute chiming sounds could represent danger, but I didn't know what to expect exactly.
I walked slowly and look everywhere really careful.
Nothing at the walls, nothing at the roof. Nothing on the floor as far as I could see.
I couldn't place the source of the sound, and it was quite fortunate that I heard the other sound. One I could recognize: scales over scales, like a dragon scratching her back or rubbing her hands. While I couldn't see anything, I stopped by instinct, just in time to avoid the rattlesnake lashing out.
I saw it just that one second, as it attacked me, and then it was gone... Except I knew it hadn't and I new it wasn't alone, because I could hear the bells. Nowhere and everywhere. A warning. A demand.
DON'T YOU DARE TO COME CLOSER.
"Okay, okay", I said, turning over my steps. But it wasn't that easy, because someone started screaming for help on the next chamber. It was my target, trapped at the other side of the rattlesnakes domains. He had reach a cavern where people gains the gift of seeing everything in its real shape. Including invisible snakes. He was terrified now that he could see them, and Rattlesnakes, the ghost kind, at least, don't trust scared people. 
That's part of the point of the warnings and the reason why you always find spooky creatures at the entrance of every known cave. If you ever have to enter, you must at least be afraid. That way the rattlesnakes will notice you when it's still time for you to notice the bells and keep your distance. If you don't, at least there is a chance the beat will keep you alive is you manage to escape before they bit you too many times.
But if you pass by them thinking there's nothing to be afraid, you might find something scary later, or end up in a knowledge chamber and gain the ability to see them: hundreds of them, happy and relaxed until they taste your fear and decide they need to kill anyone who approaches them.
If you are brave enough to try and find a way to pass through, you will surely die.
My target didn't even considered that idea, of course. He wanted me to fix it for him. And I didn't know how. When the day started over he was nowhere to be find, so I assumed that the cycle didn't affect him because of his wish, so I come back to look for him, but he never answered my call.
His host said that he wasn't in his own cycle, that he had just left. Many clients do that when they understand they can't recover what they want.
Once in a while, though, somebody claims that they saw him. Here, in this cavern, or even in knowledge chambers far away from here. They say his spirit wanders, looking for a way out, unaware of his starved body lying somewhere in the dark. Others say he's alive, that he found happiness in the caves and knows his way through them, never wanting to come back.