Gunther's hand is not bandaged nor shows any sign of injury in his scene immediately after he burns it on the stove.
Hank's last name is given as Storm in the credits, but twice in the movie he is called Hank Peterson.
When Josef Steiner knocks at Gunther's door, Gunther is reading while eating candy from an open box on the end table. When he lets Steiner in, the box is now closed.
Steiner claims the Einsatzgruppen war criminals were convicted and executed in 1945. Actually, the Einsatzgruppen trial took place 1947-48, and the only death sentences from it were carried out in 1951.
When the kid is shown doing Nazi salute on the photo, his arm is not raised to the air which is not how the salute is done.
When Gunther's victim is shown hanging upside down, she can be seen blinking.
The heating ducts (or crawlspaces - from whence the picture derives its name) are absolutely immaculate. Not a speck of dust or anything. This is highly unlikely. Lori's clothes should have been especially dirty; her yellow sock should have been practically dirty.
As the heroine is crawling through the ducts, you can tell is she being pulled (or pushed) by some device. She lifts her arms to swat away a rat, but her pace is not slowed.
When Lori is crawling at the end of the movie, some rats end up on her clearly being thrown on her by someone.
Obvious fake hand when Gunther puts it over the stove fire.
Towards the end when Dr. Gunther chases Lori in the air duct, a fishing line pulling the trolley is visible.
Shadow moves on the wall as the frame zooms in when Lori hears tapping in the ducts while she's writing at her desk.
While crawling through the vents. There does not appear to be any dirt or dust on Lori's clothes. Her sock was yellow and the bottom of it should have been visibly filthy after crawling and walking around in a dirty, dusty environment.