legends that leaving cut onions around a dwelling could ward of the Bubonic Plague...
actually during the times of the bubonic Plague
was also a time of very DEEP fear of anything herbal
and anything related to witch craft ...SO cats became
outlawed
as they were thought to be enchanted and possibly a witch was inhabiting their body to escape detection...
so that
all cats were systematically killed by throwing them in a burlap bag that was weighted with stones and then tossed into the nearest river. Only the cats kept ultimately secret beneath houses survived.
that being said:
Along came the regular merchant trading ships as trade
was booming back then and when they tied up to the docks down the mooring lines the rats ran that had crossed the ocean in the hull of the ship.
Now these particular rats were loaded with fleas and "they carried the BUBONIC plague"....so that anyone bitten by the fleas contracted the plague and of course it was contagious as hell.
the ceremonious killing of the cats based upon paranoia and superstition created a situation where the rats had no natural predators to keep them in check and being "communal" they passed the fleas from one to another thus spreading the plague carriers.
In those days there were some men that would rob the dead and they wore a string of bulbs around their necks to "ward off the evil spirits" which was actually GARLIC that repelled the fleas from jumping on them and biting them giving them immunity.
it is from this custom of wearing garlic that this legend was Born.