|First-time dog owner seeking advice from the more experienced on whether a vet visit's in order
We have a Shih Tzu who just turned 11. We bought him from a breeder when he was 4 months old. He's lived with us, in the same house, all that time.
Our son was about 5 when we brought the dog home, so 15 now. They're both pretty gentle specimens. Our son has bonded more with the dog as the years have gone on. He'll scratch the dog where he (the dog) likes, and present his face to him, which the dog will lick repeatedly, which squicks me out but we're not here to talk about *my* problems. The dog has had a pretty healthy history, with his most notable issue being corneal abrasions. I don't remember observing any incident suggesting he's visually impaired. Other than that, his jumping (e.g., onto the couch) has gotten to be a less sure thing lately, and he started wiping out on stairs often enough starting a year or so ago that we just carry him up them now.
Twice in the last couple months, the dog has given our son what I'd categorize as pretty hard nips. I didn't witness either. The first just barely broke the skin. It happened when our son went to pick him up. The dog was staring at the wall behind his food and water bowls (not new behavior, btw), and he saw our son walk in the room but wouldn't have expected he would get picked up. Our son said the turn to bite was a pretty fast move. The dog's never shown a disposition anything like that. Now tonight he nipped our son again, this time not breaking skin. He was on our son's bed, licking his feet. The lights were on. My son wanted to bring him into the other room, and approached him pretty slowly, head-on, and reached to gather the dog up, as he has many times before, with his hands at mattress level, not over the dog's head. Our dog watched it happening, and let our son get his hands halfway alongside his body, then again turned and bit/nipped him, just as our son started to put his hands actually on him. Our son says the bite seemed roughly as hard as the one that did break skin, but he has no marks from it.
The dog has let my son, my wife, and me pick him up fairly frequently throughout his life, presumably understanding that he is too cute for us not to. I cannot think of any other behavior anything like this. I'm wondering whether this is not-uncommon behavior, perhaps around this age, or whether it could be a sign of medical trouble. I can't seem to find the search phrase for this; most results are about newly acquired dogs, and/or strangers. Would be grateful for any expertise or experience.