When Dr. James Riley goes to lock the chain on the backdoor; the chain is seen looped around both door handles and the lock is passed through both ends with the lock opened. When the camera goes into a closeup of the chain and lock; the chain is now only on the right door handle (the doctor reaches through the left handle but does not pull the chain through it), and the lock is no longer looped through both ends of the chain. The doctor locks the chain up through the right handle, but when it goes back to the wide shot the chain is now locked around both handles and locked.