Angela Kinsey is pregnant in the last few episodes of the fourth season. It is noticeable some of the time, especially in her face but there is always either something blocking her stomach or she is behind a desk or table. The only partial shot on her body was when the Office employee opened the ground floor door to the carnival party at the parking lot.
Holly asks Creed what he does at Dunder Mifflin, he later on asks the camera crew what he does and says some gibberish words trying to remember his job. In The Office: Product Recall (2007), Michael says Creed's job is "Quality Assurance".
In the cold opening, Jim answers his phone and talks to Dwight's "mater" (mother) but in an earlier episode, after Dwight killed Angela's cat he says they could bury the cat in the East field by his mother.
The trivia items below may give away important plot points.
During actors Angela Kinsey and Rainn Wilson's intimate scene at the end, Angela Kinsey was pregnant. She later complained in an interview that Rainn had eaten a tuna sandwich before the scene and because she was pregnant and extra sensitive to smell she had a hard time kissing Rainn.
In the Season 4 finale, when the office workers are watching the YouTube video of Ryan's arrest, you can see the the video was added on April 16, 2008; giving a clue to when the finale was filmed, and also slightly upsetting continuity (the episode was set in May instead of April).