When Londoners started killing cats that they thought were carrying the plague. During the Great Plague of London, people suspected that cats were spreading the plague, so they started killing stray cats. However, once the cat population started to fall, the plague got even worse - because there were no cats to kill the real plague carriers, the rats.
And that would be pounds to kilos.
Planes measure fuel in weight units not volume!
#10
And no, it was the fleas on the rats that carried the plague!