Family Guy Season 5 Episode 9

The dance sequence with Gene Kelly is taken from the 1945 movie "Anchors Aweigh". The original version had Gene Kelly dancing with Jerry the Mouse (from Tom and Jerry). The animators did a great job covering Jerry with Stewie but the reflection in the floor was not changed so you can still see Jerry there. Ironically when the original was first shown, the reflection of Jerry was missing and needed to be added before general release. The animators and creators deliberately left Jerry's shadow because the reflection was vague enough to not give away that it was Jerry. However Jerry's tail reflection was sometimes noticeable and was removed and Stewie's entrance had to add a reflection.