What hides between Shadow and Light?

[Krzysiek K.]

The "hole digging creatures" refers to the hole digging creatures in the games most likely, the rock worms that is.

Considering that the new game will be most likely in entirely new setting and separate from Penumbra series, I wouldn't expect rock worms there, nor in any puzzle about the game. Also I don't see any problem with referencing bugs, as bugs are natural during development of every appliaction and they are going to stop the infestation.