Agent Cybil Bennett uses a Surefire M6 Guardian flashlight that has a temporary tailswitch with a twist on constant switch, but in the movie you can clearly hear the typical click of a click on switch.
When Rose is at the gas station, she's wearing a locket around her neck. The next time you see the necklace pendant, as she first walks through Silent Hill's main road through town, she is wearing a carabiner as a necklace pendant and not the locket. In the next scene where you can see the necklace pendant, when she wakes up in the bowling alley, it's back to a locket.
When Christopher and officer Gucci, who's wearing a blue tie and gray trench coat, come out of the building, the camera switches back and forth between Rose and Christopher. When it finally reveals officer Gucci in the background, behind Christopher, we notice he's wearing a different colored tie and trench coat.
In the beginning of the movie after Rose saved Sharon, Rose and Sharon are lying beneath a tree. The close up shows Sharon's hair in her face. The next shot from above she has no hair in her face. This is repeated a second time.
Early on as Rose is chasing Alessa/Sharon through the deserted streets of Silent Hill, she is seen passing by outside an open garage door. The camera is located inside the garage looking out. There is a blue sedan (Plymouth Valiant?) seen on the opposite side of the street. The sedan is sitting in front of a number of other garages.
Immediately after, Rose is seen passing the same blue sedan and garages this time with the camera located behind her looking down the street in the direction of her travel.
When Cybil and Rose are trapped in the room hiding from Pyramid Head, when he reaches in and starts to pull up bar blocking the door the bar hardly moves. When Cybil shoots his arm and he pulls it back the bar is way up away from the hands.
When Christopher breaks into the Brahams archives offices at about 0:59:45, the clearly visible orange anodized end caps and typical wiring on the fluorescent tubes identify them as Kino-Flo lights, a specialist type manufactured solely for the film industry. The arrangement is quite different to a conventional domestic lighting system. Orange end-caps indicate a tungsten-balanced tube; blue would be daylight.
When Christopher asks about Sharon at the garage, the mechanic is working on a Dodge Magnum with a West Virginia license plate on the front of the car. West Virginia doesn't issue front license plates.
As the miners are trying to break down the washroom door, the camera pans over the door frame from Rose's side to the miners' side. Just as it settles into its final position, you can see the sliding wall section they used to allow the camera to pan, sliding back into position on the left of the door frame.