It reminds me of my parents dog, a Saint Bernard. Dad one ended up cutting into the quick when Bruni was started and move her paw just as he was clipping the nail. It hurt, naturally, and they felt bad, so she limped and got sympathy.

Now, evey once in while when I am visiting, she will start to limp, but if you watch carefully, you'll notice that the "hurt" paw is inconsistent - it switches sides, and sometimes is a front paw, too. We tell her she's being silly, pet her a little, and the limp goes away!