This card presented the Icelandic legend of the Yule Cat. From https://en.wikipedia.org/wiki/Icelandic_Christmas_folklore#Yule_cat:
The threat of being eaten by the Yule Cat was used by farmers as an incentive for their workers to finish processing the autumn wool before Christmas. The ones who took part in the work would be rewarded with new clothes, but those who did not would get nothing and thus would be preyed upon by the monstrous cat.
The outside of the card is an illustration of a giant cat silhouetted in a pine forest against snow-capped mountains. I made the fearsome creature’s eyes red, echoed by a thick red border around the image.
On the inside, white and red type is arranged on a jet black field:
“According to Icelandic legend, Yule Cat, the Nightmare, stalks the snowy countryside in winter and devours anyone not equipped for the freezing weather. Friends don’t let friends get eaten by Yule Cat.”
A tiny hand-knitted scarf was included in the envelope. A friend knitted all the scarves in various color combinations: mostly red with white fringe or vice versa, some also in blue and white for Hanukkah.
But in teensy type at the bottom:“What’s that you say? The scarf doesn’t fit? Maybe Yule Cat will get you after all.”