Other mistake: The guys all go water skiing, towing the boat behind Peter's car. After Quagmire gets his penis bitten off the scene cuts to the hospital parking lot. Quagmire's car is parked next to Peter's. There would be no reason to go home and get his car instead of going directly to the hospital. (00:07:15)
Plot hole: When Stewie and Brian are at the diner Stewie says he negotiated a deal with the mob by telling them he convinced Mort to give him his flash drive with the info to put the mobsters in prison. When they actually meet, Stewie tells the mob guys the flash drive is "his" and that he bought the coverage. Then he says his address is on the drive so they can mail it back to him. The mob guys didn't realise Stewie lied about whose flash drive it really was. (00:15:40 - 00:19:00)
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