When Sam turns up at the baseball stadium and various characters begin kissing each other, Kristin hits Jason with her purse when he tries to kiss her. After this shot, they can be seen in the background performing the same actions.
When Josie and Sam are painting, she wipes paint on his face. In the video that everyone at the office is watching, he wipes the paint off before putting paint on her face. In the shot of them "actually" he doesn't wipe the paint off at all.
When Josie is asked to read from Act 5, Scene 2 of "As You
Like It", she opens the book to the very beginning of the play instead (although it is conceivable that she was reciting from memory and didn't need the text at all). Also as Josie's book it open to the beginning, Aldys' book it open to almost the end, and the girl shown behind Josie book it open to the middle.
As Anita is pitching her idea about a double date to Josie, she takes off the cap to her water bottle and places it on the table. In the next shot, the water is still unopened.
When the students are having the sex discussion, the girl at Josie's table is telling her that she is ready to have sex. If you look at her banana, the condom changes positions numerous times.
When the Denominators are holding their bake sale, the sign on the table for Pi reads "3.1457..." Pi is actually 3.14159265...
When Gus and Anita voice their concerns about Josie's assignment, she says, "Neither of you think I can do this." Josie, a noted pedant, would know that when used as a pronoun "neither" is singular and would say, "Neither of you thinks I can do this."
In English class, Josie is instructed to read a speech from Act 5, Scene 2 of As You Like It. However, the actress is clearly reading from early in the book, around where Act 1 would be.
When Josie goes to the Tiki Post she goes to the toilet and pulls the toilet roll, a piece of toilet roll gets snapped off the roll without the slightest pull.
When Josie has been to the club they stamp Delloser on her hand. When Josie wakes up the next morning her forehead says Loser, which reads left to right. It should be mirrored as it is a print from her hand, and should only read Loser when she looks in the mirror.
During a flashback to Josie's high school days, a student is shown pouring Sprite into her backpack. The can design shown is current and was nonexistent in the early '90s.
Josie Geller is 25 when she enters the senior class of 1999's Prom. This would have made her, if she graduated at the age of 17/18, a graduate of the class of 1991/1992. Her prom dress flashback is a 1980s outfit. She was invited to the "senior" prom, which means her date would have had to be a senior or junior to invite her, and since he was her classmate, she would also have been a junior or a senior. So, she would have graduated during the 90s, yet her prom dress is in 1980s style, and any flashbacks of her "Josie Grossie" lifestyle show 80s outfits and play to Cyndi Lauper's "She Bop" - a hit in 1984, 8 years before Josie would have graduated, and at least four years before she was old enough to be in High School.
Before the prom after Josie and Guy show off their outfits, in particular Guy's sword, you see as everyone walks into the prom, you hear Rob say, "I wanted a sword," but he is clearly smiling and not saying anything at all.
The geography teacher refers to "the island nation of Bali". Bali is not a nation; it has been part of Indonesia since 1950.
In the first outdoor gym class scene, you can see mountains in the background. There are no mountains in the Chicagoland area.
Josie is extremely smart about words, and she's constantly correcting other people's grammar. Towards the beginning, after she gets her assignment, she makes the comment, "Neither of you guys think I can do this", which is grammatically incorrect (it should be thinks). Josie definitely would have known this. Other similar examples (all in the first 20 minutes), either said by her or not corrected: "My inspiration for these stories come..." (should be comes); "can" when careful grammarians insist on "may" (Josie's offer of her LeSabre); the mispronunciation of "pastoral" by Sam and Josie (emphasis should be on first syllable); "your guys's" (should be you guys' or just your).