Fire

Did you notice how the kind of learning Strepsiades pursues so feverishly for most of the play ends up biting him in the butt, or, to put it differently, burning him?

Yup, just like early man, who ended up with fire after banging rocks around, Strepsiades bumbles around until he manages to get the learning he needs (via his son). But once the "spark" of his son's intellect is lit, things get well out of control, because the Thinkery's wisdom has unanticipated consequences. For example, Pheidippides uses his newly learned logic to justify beating his father—which is totally not what Strepsiades had had in mind.

So, apparently aware of the truism that you can only fight fire with fire, Strepsiades decides to extinguish the flames of Socratic learning by burning down the Thinkery. He draws an analogy between this physical fire and the intellectual "fire" he's trying to put out when he tells one of the pupils what he's up to. When the pupil asks for an explanation for the arson, he says, "What do you think? I'm engaged in a subtle argument with your house!" (1495).

See, get it? The joke suggests that fire is like a "subtle argument"... yeah, subtle like a kick in the pants. Hmm, maybe we need to rethink our assessment of Strepsiades's intelligence, because that's dang clever (and funny to boot).