Other mistake: When Stewie sneaks into his parents' room and attaches the breastfeeding pump to Lois, he places the cups too high on her chest for them to be on her nipples. You can see this, especially after he removes the cups.
Continuity mistake: Lois' breasts grow in size when Peter is trying to get Quagmire to snap out of his trance.
Revealing mistake: When Peter leans down to get the basketball, a dot briefly appears on his shorts, then disappears almost immediately.
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