But right behind the knee, on the X-ray, was Theo's bladder. Theo's bladder X-ray had the same little white shadows in it that Velvet's had. Theo had a whole bunch of bladder stones. They hadn't been causing any symptoms, but he may have passed one now and then and not said anything about it. That's the sort of thing that a nice dog might not mention, even if it was a little uncomfortable.
Bladder stones are different than kidney stones.
We humans are more likely to get tiny stones in our kidneys, and when they pass from the kidney to the bladder, it hurts bad enough so we tell everybody about it. Kidney stones are so small that once they get from the kidney to the bladder, they usually pass the rest of the way out unoticed. Bladder stones may be so big that they can't get out, except through a surgical incision. Some kinds of stones can be dissolved with the right diet, but not Theo's. Some of them are small enough to pass when the dog urinates.