Revealing: In the scene where Al and his Dad (both played by Ed O'Neill) are sitting on the couch side by side watch the lines of the cushion in the middle. Every time one of them moves you can see where the two separate shots are overlaid.

Deliberate "mistake": After being strip searched by the Bundys Marcie looks at her left hand and wants her wedding ring back. If you look at the strip searching closely you will see that no Bundy is in the near of her left hand. You can see the hand keeping untouched the whole time.

Visible crew/equipment: After Al fixes the roof and Peg reminds him to fix the TV antenna, when Al says he can do it, a shadow can be seen moving across the blue bucket on the table. (Probably a crew member or equipment.)

Plot hole: Al hasn't got enough cash to pay for a pizza and Peggy overmaxes his credit cards. But somehow he manages to buy three flight tickets for Chicago-Las Vegas. Where'd the money come from ?

Revealing: When Kelly enjoys her triumph at the middle of the stairs you can see a shadow on the wall right from her - obviously Al stands behind the wall waiting for his cue.