Amy will often talk about someone's "feets".
I suppose this is because she knew the irregular plural "feet" from fairly early on, and then when she later acquired the regular plural marker -s, she tacked it on for good measure, thus marking the plural twice.
It reminded me of Klingon children talking about ngopmey ("plateses", or something like that—tacking on the regular plural marker -mey to the suppletive plural ngop "plates" of jengva' "plate"). Or, for that matter, Dutch children talking about kinderen and eieren, which have two plural markers, too: -er-en. (As does English child-r-en; compare German Kinder with only the -er plural marker.)