He is known to be mute because he does not have his mouth. however, in the scene with him tripping the doorstep in The Wrong Trousers, he does a high pitched squeak. he can be heard making a similar sound in one scene of A Close Shave.
He does not appear to have any fur, which is alluded to inA Close Shavewhen Wallace says, "We've tested this (the wool-o-matic) on Gromit, haven't we, lad?" Gromit replies with a dark nod and a faraway look.
Nick Park originally wanted to voice Gromit himself, before casting Peter Hawkins. but he later scrapped his lines as he felt he didn't need to communicate with words.
Gromit was inspired by the character of Snowy from The Adventures of Tintin, and was originally to be a cat with a large toothy grin. this idea was later scrapped as Nick Park found a dog was easier to animate.