Gnomes are famous for their festive springtime celebrations. Farm villages will often dye their hens eggs bright colors; with gnomish magic, the chicks that hatch from the eggs have the very same colors. The chickens eventually lose their hues, but the stronger the magic, the longer the color stays. In a gnomish village, one can easily spot the village shaman by his flock of gaily colored fowl.
Rich Romans raised fish in private pools at their villas. A favorite fish was lamprey, a parasitic fish which sucks off blood and flesh but made an excellent meal. A particuarly gruesome punishment for slaves was to be thrown into the lamprey pool, where their flesh was ripped from the bone by swarms of the jawless fish.
Medieval Britons didn't write contracts. Instead, men making agreements would clap their knives onto an altar and recite the agreement three times to seal a deal. Even after the Normans introduced written contracts, British nobles would wrap the parchment around a knife to authenticate it.
The party is walking through the forest at night when they come upon a clearing. Half a dozen black-robed corpses lie scattered across the ground, and a pentagram of blood is shoddily drawn in the dirt.
It seems these people summoned something they could not control. Whether or not the demon returns is up to the GM, but it would be just as rich if the demon never returned, and for the rest of the night, every stray sound or odd shadow will be jumped at!