Now one of the theories was that the "slithering horror" might have been an octopus that had dragged itself up out of the sewers and later returned there.
Now I ridiculed the idea (I still do not believe that any octopus was involved) of a land octopus because despite tales I'd never seen such a thing. Now I have and you can also. Its odd and no hoax.
Then go here for scientific takes on this.