Continuity mistake: Herbert sings on his way to the Griffin house and hangs off a lamppost outside the house. Later on, a shot of the Griffin house shows no lamppost outside. (00:05:20 - 00:18:20)
Continuity mistake: The kitchen sink is completely missing. It has always been in front of the window through the entire series. (00:01:40)
Chosen answer: It's a real song called "Elvira". Originally by Dallas Fraizer in '66, however, this version seems to be the Oak Ridge Boys cover version. However, the mega lesbians skip the verse and just sing the chorus after the opening line.
Bishop73