Pain.

"Good morning, Doctor."

"Yes, yes, likewise. Please have a seat. And what is your problem exactly?"

"I have this pain."

"Pain. OK. Where do you have this pain exactly?"

I said something, but it isn't too relevant to this joke, so I'm going to skate right over it.

"Alright. How would you describe your pain?"

I'm sure we all have those moments when words fail us to the point that we consider if we've had a brain stroke at worst, or if we have severely overestimated our vocabulary at best. It was one of those moments.

"Er.. It really hurts."

"Yes, that's what pain does. Where would you put the level of pain you're feeling on a scale of 1-10, 1 being the pain of a light slap, and 10 being the worst pain you can imagine."

Whoever said pain is a non-sentient entity has never really felt pain at all because, well, at that particular instant in time, Pain spoke to me.

"Ten. Say ten," it hissed, seemingly encouragingly, but unable to hide a dripping malevolence. I ignored it while I weighed matters.

It was one of those situations where you really, really want to do something, but the pressure of keeping up appearances, specifically that of being a Real Man, inevitably wins out. I mentally cringed at Pain's impending displeasure as I said -

"Maybe about a three." Pain then had its tantrum of course. I snivelled and moaned inside because Real Men and all that.

"I see. Now then, would you describe your pain as a throbbing pain?"

For some reason, the image of Leonardo di Caprio burst uninvited into my mind. It took me a long second before I could work out the connection to the word 'heart-throb'.
"Er, not sure."

"You see, the kind of pain you'd feel four hours after you have a piano dropped on your little toe."

I studied the Doctor with fresh, startled eyes. He really did have a creepy aura to him.

"Er, I really wouldn't know."

"Perhaps it is a shooting pain. Surely you would know how somebody with arthritis for forty seven years would feel after squatting two hundred kilos?"
"Haven't you ever accidentally tripped and fallen on a rusty sword and impaled yourself through your knee?"
"Or maybe drilled a hole into one of your teeth deep enough to see gums, and then poked at it with an ice-cold fork? All shooting pains, you see."

"No. I.." It really was time to put an end to this because I didn't like the turn this was taking. "It's a kind of burning pain."

Did I misread that glint of satisfaction in the Doctor's eye? "So, I presume you've had the chance to jump into a vat of boiling water after a walk through waist-deep snow naked?"

"Something like that, yes," I said, thinking of the time I accidentally touched a hot cooker and screeched loud enough to rattle glass.

"Very well then. I would still like to confirm that it isn't a sharp pain. Or a tingling pain. Or a dull pain. Misdiagnosis would be catastrophic, you see."

That was when I noticed that the Doctor had a suspiciously long blade in one hand, and was twirling it around like a rapier. It looked finely honed, and recently too. Right next to it was a vat of water labelled 'Boiling', and beside it was a jar named 'Tarantulas'. Catching my glance, the Doctor subtly turned the table lamp to illuminate the rest of his macabre repertoire. A closed box labelled 'liquid nitrogen' was sitting right next to glass case tagged 'instruments'. They were very specific kind of instruments, and they were all very sharp. Other silhouettes pressed ominously from the shadows.

"We have to be sure, you see." That smile of the Doctor could have frozen a rampaging sabre tooth in its tracks, and that good old sentient co-habitant of my mind was no match. Pain mewled like a kitten and said, "Run."

PS: There is a moral to this story and it's that if anybody ever tells you what kind of pain they're feeling, you need to scarper like your feet are on hot coals.