After the first performance of the "Thank Goodness I've Got You" song, Olivia's dress is pink. When Stewie slaps Simon her dress changes to blue and she has make up on and then it changes back to her pink dress.
When Stewie first meets Olivia, the chairs in the classroom are orange. After his performance they change to blue, and then back to orange again.
Yahtzee is played with 5 dice not 6.
When Stewie is in acting class and re-enacting his birth, the teacher tells him to "burst through the placenta", which does not happen during a real birth.
When Olivia leaves Stewie, Simon says it is not going to work without her. But when he walks away, he disappears half-way.