The movie is obviously made in the UK, with changing accents from the actors throughout, but it is supposedly set in the US. During an item on the news, however, the headline reads 'Mutated Rat seen in English countryside'.
In the garage scene, the rat tears off a woman's hand. The woman's real hand is seen under her sleeve a couple shots later.
The guns used by the police are clearly fake as there are no holes in the barrels.