There is no reaction.

The "wall" is as warm and semi-soft as one would expect a giant animal to be. From where Walter stands, he cannot really see the end of the expanse of brown fur - as far as their torch reaches, there's the cave wall and the furry wall, going up and up and stretching on to the sides as well. There's just enough space between mouse and wall to walk there and see if they can learn more about the creature, if they dare.