"Mousies" is the plural of "mouse
", as in "I have these two three-button mousies just in case I spill the grapefruit juice on one". This avoids the awkward
situation of calling it the same thing as a plural
of the rodent
"Mouses" is what a mouser does - think Tom and Jerry: Tom is a mouser. He mouses. He mouses Jerry and any other meece (meeces?) that might populate the dwelling.
Coffee, please! Not lucid yet!