Mantis or Pistol Shrimp?

[Oscar]

Over the past two weeks I have heard some clicking in my tank. This has occured around 4:00am when the tank is completely dark except for some stray light from the refugium.

My first thought was that a mantis hitchhiked in with my rock, but I read elsewhere that it could also be a pistol shrimp.

I kind of freaked out at first although with a bit of reading about mantis shrimps I am bit calmer here today.

So a couple of questions:
1. How do I determine if the clicking is from a mantis, pistol, or my imagination?
2. If I have a mantis or pistol what have other peoples experiences regarding losses of critters and fish?