At the cemetery, Karen tells her boyfriend that burning incense is a Buddhist ritual, and that the smoke carries their prayers to the spirits of the departed. Buddhism doesn't acknowledge everlasting spirits. It is actually a Shinto ritual.
When Karen is looking up information about Toshio on the internet, the search engine option "images" on The Daily News Japan website is spelled "imaegs". Also, "option" is supposed to be capitalized like "View", "Tool", and "Help" are. "Tool" is also meant to be "Tools".
The message Susan leaves on the answering machine is a little bit different when Karen first hears it than when the detectives hear it again later in the movie, and when we actually see Susan leaving it.
At the end, before Karen enters the morgue, she has a lot of blood and bruises in her face. Seconds later, inside the room, she appears with less blood than before, especially on the right side of her face.
The two gas containers abandoned just beside the door are nowhere to be seen in the scene when Matthiew is leaving the house. In the scenes to follow they are back there especially because they are needed to move on the plot.