You see Millie just about to play the piano but in the background you see Sam starting to tap Ken to talk to him on the couch. After Millie starts to sing Sam disappears from the couch in the background with Ken. Then Sam again is seen arriving on the couch and has the conversation with Ken.
Just before the party Lindsay lays a bowl of chips on the piano, which has the fall board open. In the next shot, the bowl is on top of the television and the fall board is down.
When Lindsey is in math class, the teacher has an equation for the Simple Power Rule and the equation is incorrect. The -1 should be in the exponent of x so that x is raised to the n-1 power.
Neal claims that the Jewish Sabbath day is Friday this is inaccurate that's Islam Jewish Sabbath day is Saturday.
Nick mentions that John Bonham died the previous week, meaning that it is set in September 1980. However, a few minutes later, he talks about going to see Pink Floyd: The Wall (1982), a film that was not released in the US until August 1982.
When the guys are in the party store to buy the non-alcoholic beer, they're standing in front of a glass cooler, and you can clearly see most of the products in it bear labels and logos that weren't around until years later.
The boom mic can be seen in the shadow over the bed, when Neil reveals to Lindsay that he is in love with her.