[It's certainly no joke. Sokka's face lights up just by the fact that it's at least working to some degree. His face also lights up because there's FIRE and therefore LIGHT there. But still, that someone else is gawking over his "bending" is still pretty incredible. He feels rather proud of himself.]

I have no idea how it works! [Way to sell yourself, Sokka.] You just say the words, concentrate really hard, and whoosh! There's a ball of fire! There's a bunch of spells that I haven't gotten around to learning yet, but this is the first that's actually working!