As Don is walking through the dining room at the beginning of the episode, the light fixture over the table swinging slightly in the top left hand corner even though nobody touched it nor is there anyone else in the room.
Around 10:00 when Megan is interviewing the agent, there is something white in the Agents left breast pocket that is higher than lower, sometimes not even there towards the end of the interview.
When Oswald Kittner is being initially questioned about his baseball statistics work, he says he never showed it to anyone to maintain his advantage at Fantasy Baseball yet the FBI was only led to him by comparing his work to some posted online at a Fantasy Baseball website.