Flatmate: [watching Terminator 3] What’s phenobarbitol?
Bella: [paying no attention] It’s truth serum, isn’t it?
Flatmate: Why would a vet’s office have truth serum? To get information out of recalcitrant puppies? “You there: did you poop in the corner?“
It’s an anti-epileptic used in veterinary medicine. You may be thinking of sodium pentothal (anaesthetic) although the whole ‘truth serum’ thing is a bit of an urban myth.
it’s the stuff you use to put animals down