Factual error: In the park, Stewie and Brian are playing the "water pipes" like a xylophone. Trouble is, in order to get the tones they were playing, the glasses should have had different levels of water in them. If you look closely, all the glasses have the same level of water.
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Continuity mistake: When Peter is about to walk into the Drunken Clam, his seeing-eye dog refuses to go inside, so he puts the leash on a homeless man, thinking it was a fire hydrant. We actually see a fire hydrant in front of the homeless man, but then when Peter ties the dog up, it's gone.
Continuity mistake: When Peter and Brian are entering the Channel 5 Studio, we see a far view of Tom and Diane eating. The torn right sleeve (close to her hand) from the far shot shows that it reaches her elbow. In the close up shot, the sleeve doesn't go to her elbow.