[RyJones]

I'd guess en passant is more surprising to neophytes than castling

[jacquesm]

At a guess check-mate is the most surprising to neophytes. It gets them every time no matter how often it happens.

[lmm]

Huh? If checkmate is confusing you can just play until you take the opponent's king, with minimal difference to the game.

[Someone]

That, and stalemate ("what do you mean, a tie? You can't move, so you lose!"), but that is a rarer occurrence, as it requires the neophyte to be on the winning side (he won't complain if he is the one without a legal move, and you announce it a tie)

[mediocregopher]

I had never even heard of that (although I'm by no means an avid chess player). I think I'll have a hard time convincing my friends that's a real rule.

[jspthrowaway2]

The Wikipedia article is good at explaining the rationale. According to it, it was added around the time the two-space opening move for a pawn was added to balance the game.

Oddly, though Wikipedia deletes programming languages like Factor due to non-notability[1], editors get to go nuts on everything chess or Star Trek without recourse. If you want to know more about why things in chess are the way they are, Wikipedia is your pal.

[1]: http://en.wikipedia.org/wiki/Talk:Factor_(programming_langua...

[zem]

wow, that factor notability discussion was a depressing read.

[dfan]

Yeah, I was actually going to use en passant, but I figured more people would understand the comment if I used castling.

[RyJones]

They're both outside the norm enough. I remember the first time en passant was used on me (4th or 5th grade?), I thought it was made up.

If you want to start an argument, stop someone from castling through check.

[jspthrowaway2]

I've had people shout at me about making up rules after capturing en passant.