So it's now apparent that at least one of my dogs has a persistent and unhealthy interest in porcupines, and some avoidance training is in order. Interestingly enough, a day after Jenny's last encounter with a porcupine, and three full days after first getting quilled, I was doing a routine check for burrs and stickers when I felt a sharp jab on the upper side of Jenny's muzzle, right behind her nose. A tiny point was poking up through the skin. I gently pulled, then pulled some more, and eventually extracted this intact, inch-long quill from Jenny's snout. I had apparently overlooked it a few days earlier and it had migrated from the roof of her mouth upward, all the way through to the skin above.