Continuity: When the Sandy/demon tries the blow Rogers brains out he opens the bathroom door containing the 'floating garden tools'. The hedge cutter shoots towards Sandy/demon lopping off her head. Next scene Roger picks up the head placing it in a bin bag, but there's no blood, but there was when he shotgunned a hole in her from an earlier scene.
Great sites
Mistakes
When Rogers blasts the Sandy/demon out through the front doors we see a supposedly large bloody hole in her back, but no blood nor damage to the doors. See more...
House mistakes
Revealing: Later into the film Roger realises that his aunt's paintings hold some significance to the whereabouts of his missing son. He removes a cloth from the top left of a painting revealing an image of his son trapped in his bathroom cabinet. Note the cabinet door is the wrong way round to the one in his bathroom.
Continuity: When Roger babysits Robert, the neighbour's son, he begins to cry, so Roger sits with him and watches TV. All of a sudden the tears on the childs face miraculously dry up between cuts.
House trivia
After the cops leave Roger's house, Roger is fighting with the sandy/demon upstairs then opens the bathroom door to release the floating garden tools. There's a 1958 poster of the movie 'The Blob' at the top left of the wall - another classic horror movie.