I'm surprised the vet didn't give Rimydal or recommend a buffered aspirin. My Lab/ GR, Cody, never ever yelped or groaned either. Even when he had some surgeries or in his last days. But to answer your question, the same one I always asked my vet, is "you'll know". Yeah, right, I thought. Like I'm going to be able to make the decision to euthanize my beloved Cody. Well, just like Rachel, said, he was the one who told me it was time. And as selfishly as I wanted to keep him in my life forever, I obeyed his wishes. All I can say without going into the sad details, is that they make it very clear and you won't be making a mistake. I know that he's happy and healthy at RB and he IS always with me.