A lot of folks who aren't familiar with dog anatomy often mistake an excited dog with his bulbis glandis enlarged as "testicles" because there will be two, one on each side of the back of the penis, but this is more on the belly vs. where the testicles are. If you can't find them again, chances are the dog was excited and you really didn't see testicles. If one didn't drop, then you should at least find ONE at all times.