Revealing mistake: Connie and Sam are talking in their room, while Sam is looking at his female self in the mirror. As Connie walks back into the shot, her shadow is cast on the wall behind the mirror. This indicates she came from the opposite direction that is possible in the reflection had this not been the mirror trick. In reality, she would have been coming from behind Sam, not from in front and wouldn't have cast a shadow on the wall with the mirror.
Revealing mistake: Just after Mrs. Stiner delivers the line "My car's out front" after her father's hearing, everyone except Al rushes away from the broken window. Sam brushes up against Al's shirt sleeve, causing it to move. Al, being a hologram, shouldn't have been touched.