When they are bantering back and forth in the last minute countdown the speed of the second hand on the clock slows down. At first it is spinning at a rate of about 6 seconds per revolution but slows down considerably in following scenes. This could be deliberate considering the nature of the episode
When Number 2 is writing on the chalk board, the close up shots do not correspond to the style of writing seen on the faraway shots.
The Butler is wearing black gloves when he sits on the swing. After Number Six starts pushing him, there's a close-up of Number Two. A bare handed person is now gripping the swing's ropes.
When Number Two is interviewing Number Six for a job, the Butler brings a coffeepot over to put on the table. When the scene cuts to another angle, the coffeepot disappears.
Number Six walks toward his telephone to answer it before it starts ringing.
When Number Two reviews footage of Number Six, several alternate takes of scenes are shown instead of what was aired. Patrick McGoohan gives different line deliveries and the dialogue has been altered.
When Number Two knocks on the steel doors to prove their quality, one of the doors slightly trembles.