You probably know that the incidence of children dying of poisoned Halloween candy, no matter how hyped up by shrill moms, is basically zero ... but no one ever talks about Christmas candy. Your risk is imbibing a deadly truffle is also exceedingly slim these days, but in 1858, 200 people got seriously ill, and 20 died after eating peppermint humbugs -- which Harry Potter fans will recognize as what passes for Christmas candy in England ...
Why? They were unknowingly laced with arsenic.
Back then, food and drug regulation consisted of little more than "But did you die?" And so candymongers often stretched their expensive sugar supply with fillers like, in James Appleton's case, a mixture of limestone and plaster he called "daff." Yum! Through a series of events fit for a British comedy, however, one of Appleton's shipments of daff was unwittingly replaced with arsenic, and no one could tell anything was wrong other than a slightly off taste that was probably common in a business where people just threw random shit into a pot and called it candy until it was too late.
Amazingly, even when people started dying, it was so common in Victorian England to just get sick and die one day that everyone just figured it was another outbreak of cholera or whatever. Once people figured out what happened, Appleton's boss, his pharmacist, and his assistant were all charged with manslaughter (though not convicted). Lawmakers then passed the Pharmacy Act of 1868, requiring pharmacists to do silly things like keeping careful track of which potentially lethal substances were which.
Top image: Pete/Flickr