Lmao you know how there are fics of the wolf witchers being cursed into literal wolves?? What if the viper witchers got turned into snakes.
Enter Jaskier.
Jaskier is the kid who loved every animal and insect regardless of how ugly it looked or how dangerous it was. He purposefully sought out lizards and snakes to play with as a child and absolutely adores them. He coos over snakes the way someone would find puppies cute.
So, Jaskier ends up finding Letho, who was cursed to be a snake. (I'm thinking Vipera berus, the common European adder).
At first Jaskier doesn't realize that Letho is cursed, he only recognizes the markings as that belonging to a common venomous snake he would find all the time on the grounds surrounding the manor. (Jaskier has non human blood and never suffered from the bites he sustained). The snake doesn't seem aggressive, so Jaskier easily scoops Letho up in his hands and coos over him.
Letho is instantly enraged.
Imagine a cute little snake hissing angrily, but his bite isn't doing anything and he is essentially harmless. Jaskier can't get over how cute he looks.
Eventually Jaskier figures out that the snake is a cursed witcher, and finds Letho's gear.
Jaskier can't figure out Letho's real name, so he calls the witcher "his little viper" based on the witcher amulet he found, which depicted a viper.
Don't tell Jaskier but Letho secretly likes the endearment.
Just imagine Jaskier fawning over this larger than average adder, and calling it "his baby boy" and "his little viper." Other humans are terrified of this monster of a snake - unusually big and with giant fangs.
During the colder months Jaskier tucks Letho around his neck and under his shirt to help keep him warm. Jaskier shows Letho unconditional love.
When they run into Geralt, the wolf witcher is not happy.