Anthropomorphic cats, murderous frogs, and insects dancing by the moonlight aren’t exactly part of our Christmas card tradition today. However back in the 19th century, Victorians thought nothing unusual about sending their loved ones a grim image of a dead robin with the words “May yours be a joyful Christmas.”

Many of these strange Victorian Christmas cards are making the rounds on social media this holiday season (@HorribleSanity has shared some especially disturbing ones, like the scene of a frog-on-frog stabbing, and Saint Nicholas stuffing a kid in a sack). But where do these visuals come from, and what do they mean? Some of that significance is now lost to history, yet it’s important to consider that Christmas wasn’t widely celebrated in the early 1800s. So over the 19th century, the iconography of the pre-Santa Saint Nicholas, the trees, the presents, the snow, evolved gradually.

The rise of Christmas in Victorian England is often cited as going back to Queen Victoria, who with her German-born husband Prince Albert celebrated their 1848 holidays by decorating an evergreen tree, something captured in an illustration widely shared by the Illustrated London News. According to the BBC, the first major Christmas card dates to 1843, with Henry Cole illustrating a happy family around a dinner table. It was a little expensive for the average citizen, still the tradition caught on, so in 1880 alone, the BBC states, the new industry “produced 11.5 million cards.”

So competitive was the new trade that, as Tara Moore writes in Victorian Christmas in Print, even Alfred, Lord Tennyson was given 1,000 guineas to write a Christmas card poem. Moore adds that “there is the assumption that a culture that encourages Christmas is at least tacitly Christian; nonetheless, people of other beliefs at times found it beneficial to take part in what they saw as a celebration of middle-class values and English identity.” Some poetry and imagery fixated on the nativity story, but others were more about a cultural Christmas, often purposefully removed from religion.

And alongside, pagan traditions endured in Britain and throughout Europe. In 2013, Sarah Elizabeth Troop chronicled a few of these “Monsters of Christmas” for Atlas Obscura, such as the well-known Krampus, a sort of evil counterpart to Saint Nicholas, and the more obscure Mary Lwyd, a skeleton horse from Welsh tradition who challenges people in a battle of rhymes. There’s some influence of this on the cards, as well as general interests of the era, whether science, art, or religion. Social messages were often evoked, such as dead birds reminding people of the poor children dying in the winter streets. So while they are profoundly, undeniably, bizarre to view now, even the creepiest of Victorian Christmas greetings likely had some contemporary meaning to the sender.