This pertains to the entry I posted an hour ago. Better read that first!
I love the internet! Sure enough, a Google search for the expression “an Italian with white mice” turned up useful references. At the time in question, around 1830, the English were extremely xenophobic, so just calling someone “Italian” or worse yet “Corsican” would be pejorative, but “an Italian with white mice” probably referred to very poor street musicians, often children, who might exhibit white mice (or a monkey, tortoise or porcupine) while begging. The children were sometimes indentured and may have been “trafficked”, to use a contemporary term for the exploitation they suffered. The phrase also shows up in a novel by Wilkie Collins. So the next time you want to insult someone, say they are no better than “an Italian with white mice”! By the time they figure it out, you can be miles away!