In the beginning of the movie where Anton's mom looks up and views the words that are written on the ceiling. "I'm Under The Bed". From a view of the FOOT of the bed, the camera pans STRAIGHT up and we see that the words are written CORRECT SIDE UP, therefore, to Anton's mom, the words must have been CORRECT SIDE DOWN.

But later in the same seen, the mother has been 'iced' (killed) and, from a view point of the HEAD of the bed, the camera pans up to the ceiling. So we are now seeing what Anton's mom must have seen, but the words are CORRECT SIDE UP.