A different perspective:

...TICKTOCKTICKTOCKTICKTOCKTICK...

That constant heartbeat of a noise, like an unending polka danced by an obese woman in stilettos, had been pounding rhythmically ever since anyone could remember. Even though each beat created a minor aftershock in the clan's wall space, it faded into the background, an unquestionable element of life. Like ear mites.

Unquestionable, that is, until Simon stuck his whiskers where no mouse should tread. 

"Dad," he squeaked on an otherwise routine Tuesday, "what is that sound? Do our walls breathe?"

Monohan Mouse, Simon's distinguished father, regarded his son condescendingly. "Don't be silly," he said with a nervous twitch of his tail, "our walls are inert, nothing more than a delineation of our world. You mustn't think of such things."

Had Simon possessed any sort of sense, he would have left the matter at that and continued along the well-oiled family tradition of caution and prodigious replication. He had always displayed a perilous propensity for pondering, however, and we all know that young mice lack sense.

As a result, that previously inoffensive Tuesday raised it's fists for combat and prepared to go down in history. Simon (that little rascal) disregarded his father's sage advice and got ready to Leave. 

Vamoose. 

Pry at the Gaps. 

Escape.

...TICKTOCKTICKTOCKTICKTOCKTICK...

Simon's ears quivered as they searched for the source of the cadence that had heretofore defined his existence. It somehow seemed to come from all directions at once. Well, he told himself, I have no choice--he would have to violate every moray of mouse-hood. With that thought, the errant son attacked the wall tooth and nail. His fellow rodents barely had time to gape in horror before the tip of his tail slithered through a gnawed perforation in the the wall. 

"He's a goner," rasped cousin Edna. 

Simon was a world away from his petrified family, however. He emerged into glaring light that poured down from an impossible height. The light glinted off of an equally expansive floor. Simon would have been faced with an uncontrollable urge to zoom a zamboni across that gleaming surface, had he known what a zamboni was. Instead, his heart caught wordlessly in his throat. What was this blinding place of forever dimensions? For the second time in a single Tuesday, Simon confronted just one option. The little mouse made his reluctant way across the foreign ground, the click of his nails producing an dissonant echo.

...TICKTOCKTICKTOCKTICKTOCKTICK...

It was getting louder. Simon's exhilaration blended with the sobering realization that, for the first time in his life, he was alone. Just as his doubts were beginning to put a stutter in his gait, he saw It:

It was like nothing he had ever seen before. It towered almost to the limits of his vision. Its wooden sides reflected the glimmering mist of the forest from whence the cleft wood came. Simon did not know what a forest was. Its glass doors contained an entity that seemed to dance with Its rhythm. Simon could not discern its true shape. Its face... Simon couldn't see its face.

...TICKTOCK...

The mouse ran up the clock.