Toucan Play

Okay, so get this, the joke is all about "toucan" sounding like "two can." Your friend was throwin' bird puns at ya, and you hit 'em back with a bird pun of your own, implying that two can play the pun game. You see, it's funny because you're both birds of a feather, flocking together in the realm of corny jokes, just like you and reading comprehension.