(at around 10 mins) 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.
(at around 59 mins) 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".
(at around 15 mins) When Karen enters the house for the first time, it is clear that she doesn't remove her shoes, yet when Emma grabs at her ankle a couple of seconds later, her shoes are suddenly off.
(at around 21 mins) 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 (at around 37 mins), and when we actually see Susan leaving it.
(at around 1h 26 mins) 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.
Susan gets a call from Mathew to buzz him in. when he appears at the door not enough time had passed to walk to the elevator much less go through the building's doors, walk to the elevator, go up several flights in the elevator, and walk to her apartment.