Other mistake: The night after burying the bird, a lightning strike projects an image of the tree outside onto the bedroom wall. However, the silhouette has nothing to do with the tree's shape.
Other mistake: In the first shot when Carol Ann is being put to bed, the wicker headboard is backwards. I know this for a fact because I used to have the exact same headboard (queen size), and the large support frame faces the wall. The only thing you're supposed to see is a bunch of single swirls in the front. But they probably turned it that way so Carol Ann would have something to grab onto. White wicker furniture was very popular and cheap in the 1970s.
Answer: Ectoplasm.
Phixius ★