In series "Stranger things" season 1, How were two worm holes (Ones that would open doors to parallel universe or Up-side-down) created? To be specific, How was wormhole in the base of a tree in the woods created?
Remember the tightrope and the flea explanation... the monster was the flea.
The monster was able to cross between the realities, he would tear through to get something, but those holes would then close up again. They wouldn't be used a second time.
The only holes that were shown were the one in the lab (right after the failed experiment with Eleven in the isolation tank) and the one in Will's house (the monster rips the wall open).
While searching, Nancy and Jonathan find a wounded deer. As they are about to perform a mercy kill on it, the creature drags it away.
Obviously the creature created that portal in the tree, but it is not shown how it was created.
The Demogorgon also snatches Barb from the swimming pool, but it's not shown where did he come from.