I don't know why but I was thinking about the word "mog" and wondered where it came from, and whether it is a "real" word, i.e. one I could find in the dictionary (turns out yes). With the help of the Oxford English Dictionary and Wikipedia I managed to piece together a possible etymology.
mog < shortened from moggy
moggy < regional dialect, a young woman, variant of Maggie
Maggie < pet form of Margaret
Margaret < late Latin Margareta
Margareta < classical Latin margarita, a pearl
margarita < ancient Greek μαργαρίτης (margarites), pearl
μαργαρίτης < Persian murwārīd, pearl
murwārīd < an old Iranian word meaning something coming from a shell