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.
Number Six walks toward his telephone to answer it before it starts ringing.