I've been working for most of the year with a guy who's pretty smart, but has had the misfortune of writing mainly in PHP up until now.

So we've written a lot of Perl code this year, and it's been a lot of fun as I show him all sorts of different nifty idioms, like initialising a hash slice with an empty array to autovivify hundreds of keys in one statement.

We often pair-program, and when I'm at the keyboard and I write something unusual, he just starts to laugh and say "no! don't tell me you can actually do that!"

The thing is, even if he has never seen the particular construct before, he can usually figure out what it is going to do, like an lvalue substr. It's been a lot of fun, certainly on the teaching end.