Every night at 2:17 someone knocks three times on my apartment door.
Tonight the third knock came from inside my bedroom.
The first sentence creates a stable assumption. The second does not merely surprise; it changes what the first sentence meant.
It follows the house rule: exactly two sentences, with the turn doing more than adding a monster. It changes the reader’s interpretation of the setup.
Motion Alert
The motion alert showed a woman standing motionless in my backyard at 2:11 a.m.
Face ID
My phone unlocked with Face ID while I was asleep alone in the apartment.
Smart Lock
At midnight my smart lock notified me that the front door had been opened with my fingerprint.
The Peephole
The hotel rules said never look through the peephole after three knocks.
Late Checkout
At checkout the clerk asked whether the woman in my room would also be leaving today.