When the professor writes "Djinn" on the blackboard, the line he draws underneath is nowhere near the cursive writing on the board. After the walks around the room and goes back to the board, the word "Djinn" is different with the line underneath cutting into the cursive writing.
The streets have puddles in them when Alex and the "angel" are driving away from the Djinn, and later on the roof of the building there are puddles, even though it did not rain at any point in the movie.
When the professor's face is taken off by the Djinn, instead of seeing muscles underneath, you see his real face covered in fake blood. It's especially noticeable around his eyes where there's hardly any fake blood, so you see his eyelids and eyelashes. You can even see his right eye move underneath the eyelid.