Snakes only produce a small amount of venom and it takes days to replenish reserves. They have fine muscle control over how much venom they release and scientists have measured them releasing amounts of venom relative to the size of their target.
Not sure how aware they are of doing it but I wouldn’t be surprised with all of a viper’s sensory organs that they knew venom would go to waste on a prosthetic
https://youtu.be/5nPIQiX-ukg?si=UNlRENogkmFlsqyF