Is it a worm? No, it's a tiny snake!
A western Threadsnake. And, yes, that's it's fully grown size.
The tiny guy was found slithering on the tile in our hallway, but not getting anywhere fast. Threadsnakes usually live underground -- this one must have squeezed it's way through a crack in the floor and tile grout to find his way inside, so was likely very lost. After getting him to pose for a few pictures, he was gently released outside where he could find his way back underground.