Continuity mistake: In "The Alliance" (1-4), Pam says that the next office birthday is Meredith's, but it isn't until the next month. Later, in "Survivor Man", it is said that Meredith's birthday is at the end of 'Birthday Month', when many employees have birthdays close together. It wouldn't be possible for Meredith's birthday to both be the next office birthday but also at the end of the following month, which is stated to have many other birthdays in it.
Continuity mistake: In 4-14 "Goodbye, Toby", Andy Bernard invites his parents to the going-away party for Toby Flenderson and introduces them as "Andrew and Ellen Bernard." But in 6-16 Andy tells Jim that he was originally named "Walter Jr." after his father and that it was changed when his little brother was born and the name Andrew was one that they got out of a baby-naming book. Additionally, in 8-4 "Garden Party", Dwight is introducing the entering guests. When Andy's parents arrive, Dwight says, "Mr. And Mrs. Walter and Ellen Bernard."
Character mistake: Meredith admits during the ethics seminar that she has been sleeping with Bruce, the HammerMill rep, for discounts on paper/paper supplies for the company, as well as Outback steak coupons, for 6 years. But, Dunder Mifflin did not begin selling Hammer Mill products until Season 3 Episode 2 The Convention when Michael got the contract.
Continuity mistake: At the end of the episode, we are shown a video of Dwight getting splashed with the milkshake from the point of view of the guys in the car. But it splashes differently the two times we see it. The first time it hits his lower body, and on the video, it hits him in his upper body.
Continuity mistake: Nellie and Pam are driving along, discussing what to make up about people's ancestry. Here, we see the same background go past Pam, a driveway with a black SUV on the right, and a white SUV on the left. This shot is only repeated in the angle where we can only see Pam, and the view out of the passenger side window. The car is driving along as normal, we see the two cars on the driveway, and then the car turns a corner, and we see the same shot all over again.
Character mistake: As Michael is getting ready to propose to Holly, he stops in the foyer and says, "This is where Toby announced that he was going to Costa Rica. Happiest day of my life." This is a discrepancy, as Michael was in New York partying with Ryan and Dwight when Toby made this announcement.
Continuity mistake: When Jim is outside comforting Pam after she finds out her mother is dating Michael, he begins to explain a mallard recording device that Dwight gave to him and used a big hand motion that put his hand in the air. In the next shot, the hand that was in the air is now gripping his coffee cup.
Continuity mistake: After the banker asks Toby if there is any inappropriate behavior, a few seconds later there is a flash back of Season 3 Ep. 22 when it is the beach games and Michael is hosting a hot-dog eating contest. Michael says to Phyllis to "Dip it in the water so it'll slide down - your gullet more easily." In the flashback version, everyone says "That's what she said." In the real version, no one says anything. Not to mention Toby wasn't actually at the beach day, Michael told Toby to stay because "Someone needs to stay at the office."