I guess it depends on how you define parts. I don’t consider products the body makes in this question but which are not attached to the body (saliva, urine, feces), it has to be things physically attached to the body.
Parts of the fingernails
tooth enamel and dentin (I think only the pulp feels pain)
Wow, that’s hard to imagine that the brain would not feel pain. Interesting.
If a 6-inch steel nail suddenly appeared inside my brain, I imagine I’d be rolling on the floor in agony. Of course, I might be dead, but it’s still hard to fathom.
The walls of blood vessels are exquisitely sensitive to pain, in particular if those walls are stretched. There are blood vessels running through your head and brain. When they stretch, you can get gruesome headaches. Some people seem predisposed to have this happen a lot. That is what migraine headaches are.
I have often seen it claimed that the internal parts of the body have no pain receptors; you only feel pain at or near the surface. This is obviously bollocks.
Heart attacks (especially of the “Hollywood style”) are said to be exquisitely high on the pain meter. You can look up threads right on this board about kidney stones. Ever had gastritis or “heartburn” (esophageal acid reflux) or a tummy-ache or a wide-awake colonoscopy? Ever had a bone broken?
Our OP Wesley Clark asks a very reasonable question, and he seems to have a clue that the correct answer is: Very few.
When undergoing brain surgery, patients are usually only given topical anesthesia in the area of the incision. The patient is kept conscious and sometimes needs to give feedback to the surgeon on what kind of things they’re experiencing.
There’ve been a number of people who’ve caught a nail from a nail gun in the brain. Some weren’t even aware of it at the time. It’s not that it’s not serious, just that they can’t feel it.
See** Senegoid’**s explanation above (pressure in diluted blood vessels). I have (thank God!) never had a liver biopsy; but I’m told they only use a local anaestetic on the skin and then stick the needle right into your liver - without any significant pain.
I believe what the OP was asking is more like: Which parts of your body could you prick with a needle without feeling a thing?; rather than: which parts of your body can, if worse comes to worst, hurt like hell?
I read on Wikipedia the other day that bone doesn’t have pain receptors. However, the material covering it does, hence breaking bones is very painful.
When I had to inject anticoagulant into my legs sometimes this was rather painful and sometimes not at all. The former seemed to be correlated with bleeding. (Which is all kinds of fun when you’re on bloodthinners.) Eventually I learned to probe for non-painful sites.
And the tongue is certainly not on this list… I’m looking forward to being able to eat and brush my teeth without having to take painkillers first.