Rudy was smart enough to quickly back off and minimize his damage. Some of the fiercer hunting dogs don't, and really get a faceful of spines. Porcupine quills are nothing to trifle with. The thick, hollow spines are retrorsely barbed, or beset with hooks that point backwards. This means the quills will slide into flesh with ease, but you'll have a painful time trying to pull them back out. A big porcupine might have 30,000 quills, so they've got a lot of armament to defend themselves with.
Porcupines are mild-mannered and have to be pushed hard before they deploy their quills. If an animal is dumb enough to invade one's space, the porky will try and lash it with its tail, and a strike will release a barrage of the easily detached spines. Amazingly, there are at least two species of predators that are adept at flipping and gutting porcupines, the fisher and wolverine.
The other problem with looking inside the den is that jumbo pile of scat. You'd essentially have to be laying in it on your back, and while I'll go to great lengths for you, the reader, I won't go that far. So, I turned my camera's flash on, and stuck the trusty old Panasonic right into the tree, pointed upward, and pulled the trigger. The result, as seen above, is a like a virtual colonoscopy of the den tree. As you can see, the hollowed out trunk extends up for some distance, but in reviewing the photos on my camera's view finder in the field, we could see no evidence of the porcupine.