When John meets the Exterminator his t-shirt is covered with sweat stains from the intense heat. When John sits down, his shirt is completely dry.
When Moxy, the dog, is given a shot of liquor it changes levels between camera shots.
When they first go into the sub-basement Warwick puts grease on his face and its there throughout the movie. Later on in the cave full of bones, all the shots of his face show no grease whatsoever.
The rat, who is called Doris, is male.
As Nordello is staggering down the hall of the office after breaking into Warwick's desk, muttering, "This'll teach you to fire ME", her voice is different compared to earlier in the film, and her lips aren't moving at all.
In the scene where they find the trap-door and climb down, right before the one lady falls, a man in a floral shirt is clearly visible on the right hand side of the screen sitting there in the dark.