Stupid question but...
What do the rats look like?? Do you even see them in the film?? I can't find any rat pics from this film.
sharethey kind of just look like rats. i think they mainly used models and forced perspective to make them threatening.
http://www.badmovies.org/othermovies/gnaw/gnaw6.jpg
here's a look at one of the puppets they used for actual human interaction.
http://3.bp.blogspot.com/-jTC5rOt7IVg/T0b4B2S5MEI/AAAAAAAAGPw/d9Ms0dIU w-4/s320/vlcsna47.jpg