Continuity mistake: The password needed to access Leo Bressler's hard drive, Umbellularia californica, is visible in the book. In the next shot 'umbellularia' is incorrectly typed into the password box as 'umbellurlaria', yet it gains access to the drive.
Continuity mistake: In the scene when Liam Neeson wakes up from unconsciousness following his car accident, the nurse writes something on her notepad with her right hand, but in the next shot the pen has suddenly switched to her left hand as she puts it into her pocket.
Character mistake: When the EMTs are resuscitating Dr. Harris, they use a defibrillator despite their being on a wet metal dock. Not only is this highly dangerous to absolutely everyone present, it would be completely ineffective at restarting his heart as the water and the metal would dissipate the electric current too much for it to do any good. At the very least, they would have stabilized his spine then moved him to a dry surface before beginning defibrillation.
Throughout the movie if you look in the background at the various graffiti tags, one in particular stands out. Look for the tag OZ. In almost every scene that has graffiti on the walls you 'll see it somewhere in the background, sometimes more than once. Although it is common for graffiti artists to leave multiple marks in multiple areas, Berlin is a big city and it can be spotted too often for it to be coincidence.
Dr. Martin Harris: Do you know what it feels like to become insane? It's a war between being told who you are and knowing who you are... Which do you think wins?