Slight of hand. There's nothing that makes me smile more than a plot twist I never saw coming but that makes perfect sense, or a joke that comes out of nowhere, or a moment of writing that's so pure, so perfect that it just hits you like a freight train. Although the only examples I can think of at the moment are, embarassingly, all from movies:
-The last five minutes of Little Miss Sunshine.
-The moment in The Village where the characters run out of world and, conversely, how much more sense everything you've seen prior to that makes.
-This exchange from Paul Anderson (Not the MAGNOLIA guy)'s first movie, SHOPPING:
'I know my rights, I've seen LA LAW!'
'Is that supposed to be funny?'
'Actually it's more of a comedy drama.'