When the Hobo is at the apartment getting beaten up, he gets his back stomped on with skate blades that cut his clothes and back up. In the following scenes, he is wearing the same clothes but the shirt is no longer cut, nor are there any injuries to his back.
When the bearded doctor is hanged, his blue medical scrubs are clean and whole when they should be blood-stained and torn (as they were a moment earlier) from having the back of his leg sliced.
When the bad guys approach the school bus, the rear exit door window clearly has no "PORTE DE SECOURS" sign on it (which is French for Emergency Exit). But just a moment later when the kids inside try to escape the burning bus, one of the kids can be seen at the rear exit door, where now can plainly be seen the inscription "PORTE DE SECOURS" on the window.
The school bus's emergency exit door has no signage in the window before Ivan and Slick enter but once Ivan fires the flamethrower inside, the back of the bus is shown and the door's window now has a sign reading "Porte De Secours" (Canadian French for "emergency exit") on it.
The manhole cover wrapped around the man's head is obviously fake and made out of rubber. It flexes a few times.
In the credits, they credit actor Robb Wells, as "Rob Wells" which is wrong since his name has two b's.
When Logan is stuck in the sewer, the manhole cover prop can be seen moving as it is made of rubber.
Where Slick is about to saw at Abby's neck, the blade on his saw is quite shiny and obviously real. In the next shot when he holds the blade to her neck, the blade is quite dull and flexes obviously, as it is made of rubber.
In every shot where the hobo fires the shotgun with both hands in frame, he never actually pulls the trigger, he just jerks the gun backwards.
At 7:18 into the movie, when Logan's head is severed and rolls on the ground, one can clearly see it's a fake head as the neck is cut clean and looks like plastic.