Amy was eating maize out of a tin the other day and said, at one point, "My maize are wet!" (referring to the water at the bottom of the tin).
I wonder whether the analysed the final /z/ as the plural morpheme ("mays"?)? I suppose it makes a certain amount of sense, since you're typically eating multiple grains of maize. And there's precedent, too: from count-noun "pease" to mass-noun plural "peas" with singular "pea".
The test would be to see whether she ever talks about eating one "may", I suppose.