Note that in what follows I've tried to be as sensitive as possible to the person in question (not that they'll ever read this, but since they've not asked me to put personal information up, anything remotely identifying in what follows I've changed).

An acquaintance was recently involved in a serious car crash. After a week in an induced coma, he was recently taken off sedation and is now suffering a type of post traumatic amnesia. I currently visit every day, and find that while I can almost have a conversation with him, the conversation seems random; his brain will insert responses to questions that fit the direct question, but often they don't follow the conversation as a whole.

Due to the nature of the crash and a few other things, I'm not trying to make him face the car crash or remember anything - just be there, a familiar face and voice. Often I'll just go along with whatever he's said in his conversation rather than refute it. I doubt that has any therapeutic merit, but the discussions do make for an interesting look at how, it appears, he processes conversation in this condition.

Many times the answers will seem to have been picked because they're related to his old habits, or will diverge to habit questions.

My acquaintance has/had a significant drinking problem.
Me: "What's your favourite book?"
"Treasure Island. Isn't that the one with the bourbon inside?"

My acquaintance liked playing some violent computer games, so bullets and machine guns often come up in conversation.
Me: "What are you looking for?"
"My bullets."
"What do you need bullets for?"
"To put in my dip."

or
Him:"Have you seen my machine gun?"
"No. I didn't know you had a machine gun." He looks around for it, "what kind was it?"
"A big one, you know."
"What do need a machine gun for?"
"You know, for selling and stuff."
"Where do you get machine guns from?"
"There's this guy."

When initiating conversation of his own, he will usually ask questions that are related to habit. I often think that when I go out the door, there are only three things I've always got on me - my keys, wallet and mobile phone. So it's natural to always want to know where they are.

Where's my wallet?
Where's my keys?

He was a shift worker, on a casual/on-call/rotating shift.
Is there a shift tonight?

Then there's just some really weird stuff.

Me:"Good morning."
"Where am I?"
"Hospital."
"What's my name?"
I tell him his name. "What's my name?" I ask in return, and he responds correctly.
<pause>
"I need new legs," he observes.
"Why? What's wrong with these ones?"
He jiggles his legs. "They move."
"It's good they're moving. They sound like keepers."
"Huh."

Nurse:"Do you know where you are?"
"Um, Invicible Land.
"No, try again, do you know where you are?"
"Germany?"
"No," she replies gently, "you're in hospital."
Shocked expression.