Elly's convenient hearing.

You can't fail to notice one thing about life in the Patterson house: Elly has distinct problems dealing with her daughters. I know I've said this before but it bears repeating. She's always seemed to me to be decidedly unsympathetic to Liz and April's concerns. I remember a sequence long ago when Liz first started wearing eyeglasses. As I recall, she accidentally on purpose lost the things and Dear Old Mom kinda jumped down her throat. If Michael were in the same situation, she'd start howling at the moon about the unfairness of her precious little angel being cruelly forced to wear spectacles, but since it's only Liz she didn't give a damn. I can think of any number of situations where she says to no Liz (the motorcycle, her outrage at the fact that Liz's schoolwork comes before her own selfish need to fois April off on her, etc..) that she'd bend herself awkward to placate Mikerobe. When you consider that the Pattermanse is a cesspool of barely-hidden preversion, it should come as no surprise that Elly thinks of her daughters as competition for John's love. Factor in her own regression to childhood, it's even less surprising that it's a battle to the death.