Them: Hey sir, you'll never guess what. I looked in my wardrobe and there was a whole other world, with a witch and a lamppost and a talking lion.
Me: Did the lion have some good news?
Me: Sorry, that was a subtle theological joke. It probably doesn't work if I have to explain it.
Nevertheless I did indeed explain it*. It didn't really work. However I think they got the idea of reading (or watching the film) in your bedroom and this opening up a fantasy world, albeit in your head rather than in your wardrobe.
* The pupil was referencing The Lion, The Witch and The Wardrobe, which as part of the Chronicles of Narnia contains much Christian allegory of varying degrees of obviousness. Aslan, the lion, stands in for Jesus**, who brought the gospel or "good news". I honestly don't know what audience would have actually got that joke.
** Also for other aspects of God and occasionally other prophets and patriarchs.