Alice grasps the knife in a normal cutting position, with her thumb at the front of the handle. But her grip is different as she takes it behind the curtain: the knife is now held below her fist, with her thumb at the back of the handle, in a stabbing position.
A policeman stops the cab with a fleeing Tracy, and the officer looks into the cab standing no more than a foot from the bumper. When the panicky Tracy flees the cab, the bobby is ten feet from the taxi's front and is facing in the opposite direction.
Alice's hair is different on multiple occasions on switching camera angle close-ups. Most noticeable when Crewe is attempting to assist Alice button the back of her dress...and in Scotland Yard right before Alice and Frank stroll down a long hallway.
When Alice "unlocks" the door to the building where she lives, it starts to open as soon as the key reaches the door. It was clearly not only not locked, but not even latched. However, she goes through with the motion of unlocking it.