Standing there, braying out of fear an panic of being turned into such an animal, his ears, with the increased ability to hear, picks up the sound of a car pulling into the driveway!
Shutting himself up again, he tries turning himself around in the bathroom to face the window, which looks out on the driveway.
He takes a couple of minutes to begin turning his body around, and as he does so, becomes incredibly disoriented, due to his strange new eyesight, with lack of colors. So he stops trying to move the rest of the way around, and stands there for a minute.
Then, he hears the downstairs door open up, and quickly whips around to the window to see who's car it was. Looking out the window, the only thing he sees is a world without color, and what he knew to be trees were mostly dark-looking blobs. He could tell there was a car in the driveway, but couldn't make it out very well.
Hearing someone climbing the steps, and enter into him and his brother's bedroom, he realizes he never locked the bathroom door while he still had hands! Trying to say "Oh shit!" and forgetting he cannot speak, he lets out a loud "HEE HAWW!" instead!
He hears a voice from the bedroom say "What the heck!?" and suddenly the door opens up.
Using his long neck in order to look back directly behind himself, he sees his ugly donkey body most prominently, but most importantly, he sees the bathroom door open, with someone standing in the door frame. Who was it?