Continuity mistake: At the very beginning of the film, Anton's mom and dad are lying in bed together talking. Right after Anton's dad explains to his mom how "Anton never even helped me with the Halloween decorations", he turns the light out and lies there with both of his hands behind his head. A split second later, Anton's mom looks up at the ceiling and sees the words "I'm underneath the bed" glowing on the ceiling and begins screaming. The camera pans back to Anton's dad, and both of his arms are at his side.
Audio problem: During the scene right after Anton runs into the scarecrows in his house only to find out they are his deceased mom and dad, you see him run out to his porch and begin throwing up into his bushes. You can hear the sounds of liquid hitting the bushes, but you see nothing coming out of his mouth (there is enough light in the film to determine this).
Answer: He was either too high, sleepwalking or under the evil hand's control.