I didn't explain the plot very well... red man likes trees a lot, and he is looking for the asbestos tree, since when he goes to the shop the asbestos tree is introduced, and he goes to find it in the tunnel, but then he gets stopped by the spiders, so he doesn't find them. Then he has to scare them off somehow... Its intentionally vague and the ending is a reference to when my friend did "the worm" once and it looked funny.
In the part where he grows big, this is a reference to red man 2, where he also grows big off camera after seeing a future version of himself. So red man can grow into a giant.
Really i'm glad for this reply, since everyone else wrote "haha I was so high when I watched this LOL". I was reminded of other animations that don't really tell you anything so its all a guess what the concrete basis of the story is, because I like watching those.
I hope that I can resolve it with the next one