Lavender

From the introduction:

A hole is torn in the fabric of space. Sickening vertigo grips you as you watch this violation of reality take place. You can only watch dumbfounded as the wrongness devours half the waiting room, most of the furniture, and the screaming receptionist. Absurdly, you can only manage to think, "I shouldn't have changed dentists." The gap in the world stabilizes, and anybody that hasn't already fled the room stumbles away in terror when the tear gives something back.