Did the huge snake thing that tried to eat Timmy die and get eaten by the giant centipede things?
No. The huge snake (The Lady) is on the other side of the Durshone Wall, where the centipedes can’t go…the centipedes were only able to cross the road to the fields beyond because the wall had already curved around to the West (ended going North) when Timmy and Romber passed that way. The Centipedes were eating a dead Boar, if you must know, but that poor animal does not otherwise come into this story. The snake – the Lady – will be around for quite some time.
