Well, he probably won't hear you knocking at the door. Throwing it open might lead to an embarrassing situation, or a painful one if he has like.. one of those door mirrors and he's checking himself out in front of it or something. Lightning fast guaranteed toenail removal!
Maybe still head over to take a peek through a gap or the keyhole or something.
Not that doors these days have cartoonishly huge 19th century-style keyholes that you can actually look through anymore but hey.