When Philip exits the psychologist's office he's suddenly seen wearing glasses.
The window in the background during the dinner is suddenly closed at the end of the scene.
The position of Philip's left leg suddenly changes between shots when he visits the psychologist at the beginning of the movie.
When Väktaren enters the house the shovel suddenly disappears from Philip's hand and reappears in the hallway where Joseph later picks it up.
The amount of dirt and slime on Carl changes between different camera angles when he grabs Sarah's medallion.
The book the knight is holding in the prologue is obviously a modern hardcover book. It even has a bound bookmark clearly visible.
In the shot where Carl grabs hold of Sarah's medallion director Jens Wadenius foot is visible in the lower left corner.
Reflected in the car when Philip and Carl drives away in the beginning of the movie.
It's established in the movie that cell phones exist since at least two of the characters in the movie have one (even though the psychologist's cell phone is a modern smart phone and that some time may have passed between the events at the cabin and Philip's visit to the psychologist's office it is obvious that Carl has one). Despite this, none of the four friends calls for help (It can be speculated that there is no reception in the cabin area but there is no indication of this in the movie).