1 Kyros: Oh... I just remembered. I need some more sulphur and bat guano for spellcasting.
2 GM: Uh oh... here we go...
3 Lambert: Want to go back to the village and get some?
3 Kyros: Nah, I'll pick it up later.
4 GM: {astounded boggle}

I wrote in my script for this comic that my expression in the last frame was [boggle].

Sulphur and bat guano are the material components for the spell Fireball from good old Advanced Dungeons & Dragons. (From the days before we had to call it "First Edition", because there were no other editions...)

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2014-05-28 Rerun commentary: Sulphur and bat guano are appropriate components for a Fireball spell because they represent two of the three necessary ingredients for making gunpowder - a nice explosive compound. The three canonical ingredients are sulphur, charcoal, and saltpetre. Saltpetre is the old name for potassium nitrate, and one of the traditional ways to collect this chemical was to scrape it up from caves, as it crystallised out of... you guessed it, bat guano.

So even in a pseudo-medieval fantasy setting in which gunpowder had not been invented, the wizards were definitely on to something.