Unknown secret in The Founts - ghost is pointing to the floor?

Hey look, a post about The Founts that isn't just "help am stucc :(((("

The ghost is pointing to a secret in the floor (the same place as the rune wall). I can't see anything nearby, and even after like half an hour trying to figure it out, my buddies couldn't find it either.

Anyone know what's going on with this?