"Don't you get bored playing that game all the time?"
I wasn't sure how to answer this, but a friend on irc pointed out that it's like different episodes of the same TV series. So we had a brief discussion about the paucity of locations and characters in the original series of Friends (two flats, the coffee shop, and six people, iirc).
"And I play different characters. Like, this one is a thief, and she was originally an assassin but I decided she wasn't actually evil. So I'm going to make another character who is an evil vampire assassin."
"Oh. Why have you picked those plants?"
"Because you can make potions or poisons from them. They do useful things." [Shows Mum the list of effects for each ingredient that I just picked up, and explains what they all mean.]
"Why did they disappear when you picked them?"
"Mum, when you pick apples off a tree in real life, they're not on the tree any more, are they?" (I didn't mention the fact that in Oblivion, flowers and mushrooms DON'T disappear when you pick them, because the game is Weird.)
"Why are you walking around with all that fish when you don't eat meat?"
"Well, firstly, it's impossible to be vegetarian in any of these games. They haven't invented soy mince yet. And look at my character. She's a bright pink lizard person who can breathe underwater. Don't you think *she* would eat a lot of fish?"
"I like her boots. Can you get me those boots out of the game?" <-- MY MOTHER IS SO RANDOM! She liked the Leather Boots, but the Vampire Boots were even better. Don't ask.
She did ask a really sensible question though, which was how do I decide which items to keep and which ones to sell. So I showed her the prices for each item, and the damage caused by each weapon. She asked whether more expensive weapons were rarer, and I said "Often, yes, but not always", and showed her the special Daedric quest items which I just happened to still have on me because I was on my way to build a new house.
Also, after I bought ground in Hjaalmarch to build whatever the Hearthfire house there is called, she asked how I got the items to make it.
"I dug up metals from ore sites that I found in the ground, and melted them into metal ingots. Then I stood at the anvil and turned them into nails and hinges."
"...But WHERE did you get them from?"
I didn't understand that question, so I just pointed out an ore vein next time I went by one. I guess I should have shown her ALL the pockets of the invisible bag, because I'd shown her Weapons and Clothes and Food and potion Ingredients, but not the Miscellaneous dump where everything else is put.
It's really weird explaining something that's obvious to you and completely un-obvious to someone else :O