Adult Fear: Bucketloads of it. Imagine that such a nasty family lives in your neighbourhood. Or that your baby will be born with such horrible deformities. It's even present in-universe with Scully's uneasiness and anxiety over the issue.
Evil Cripple: A hissing limbless mother of the incestuous Peacock clan. She approves of her sons murderous behaviour. In her eyes they are only protecting their family.
Evil Matriarch: Mrs Peacock. She's involved in incestuous relationships with her sons. One of them is the father of the other two. Ugh.
Shout-Out: To The Andy Griffith Show. When Mulder expresses his desire for idyllic life in an American wholesome town, Scully says it would be like living in Mayberry. The local Sheriff's name is Andy Taylor (Mulder is kinda excited and asks if that's for real). His Deputy's name is Barney. But not Barney Fife (which Mulder hoped for, apparently). It's Barney Pastor.
Soundtrack Dissonance: "Wonderful, wonderful", a cheery tune by Johnny Mathis is used for a horrible murder and son/mother mutant sex, trying to conceive another child in a rocking car and all.