Throughout the entire movie blood is spraying and gushing out of people getting killed, but whenever the ground is shown there are only a few drops of blood. The amount of blood being shown would create puddles on the ground.
In the scene where Mika gets back into the car in the parking garage of the warehouse, when the Ninjas start to attack her car and she starts it by pushing the start button, the Tachometer swings to the right and appears to "rev up". Therefore the sound effects man put a revving engine noise into the scene. The tachometer going to the right is just a test at start up of the car.
Early on in the movie, Mika drives a Volkswagen Eos. Later on in the movie, this car inexplicably changes to a Volkswagen CC (Passat CC in Europe), as seen in the chase/crash scenes out of the warehouse.
In the final fights with Raizo, Takeshi, and other ninjas, Raizo kills the ninjas and blood is shown. In subsequent shots of the whole setting during the fight, the blood disappears and reappears subsequently.
In the scene where Mika enters her home after the power cut, as Mika enters the apartment she shines her torch into her home whilst shutting the door behind her. The light clearly reflects off the camera and lights up the corner of the room behind her.
When Raizo gets Mika's photo, he reads her address in Berlin on the back side: "Mika Coretti, Götzstr. 165, Alexanderplatz, 10179." When Mika reaches her home in the night we see a street sign named "Motzstrasse". Götzstrasse has the postcode 12099, Alexanderplatz has 10178 and Motzstrasse has 10779. Both streets are not even near Alexanderplatz: Götzstrasse is in Tempelhof district, Motzstrasse in Wilmersdorf district.
Europol is a relatively small organization without executive powers, established to facilitate information and intelligence sharing between Europe's various national law enforcement agencies. It does not conduct criminal investigations, operate prison facilities or command paramilitary units.
In the hotel, Mika tells Raizo that she doesn't smoke. Later in the movie when Raizo is recovering on the bed, Mika is seen smoking. However, this due to her doing what Raizo had earlier done for her, masking her scent with smoke from a cigarette.
Since Mika gave Raizo the homing capsule, his former ninja colleagues shouldn't have been able to leave the country with him. However, the authorities would have had to let the clan take Raizo back to their home dojo in order to locate it.