I got that feeling once, I heard an odd clicking sound usually at night. I spent many nights trying to locate the culprit and I finally found him after a week.
At first you might mistake it for a worm, they'll only be about half an inch long but you'll soon realize your LR gave you the gift of a Mantis Shrimp that after several months of having his own tank I believe is a actually a Peacock Mantis. By far the coolest critter I have ever owned. He is actually trained now to eat from a skewer and won't go after snails, hermits, or fish.
At first you might mistake it for a worm, they'll only be about half an inch long but you'll soon realize your LR gave you the gift of a Mantis Shrimp that after several months of having his own tank I believe is a actually a Peacock Mantis. By far the coolest critter I have ever owned. He is actually trained now to eat from a skewer and won't go after snails, hermits, or fish.