Quote Originally Posted by kriklaf

I'm guessing it's a thermodynamics joke--you know, energy is conserved.
U=Q - PdV
V casts fireball, which takes a lot of energy. There's not really any PdV work done here (although I guess you could argue that a charred ogre has less volume than an uncooked one), so the energy cost for the spell must be the heat added-Q. Thus the heating charge.

Oh, dear. My inner physics geek is showing. Wait--did I say inner?
Not to be technical, but two issues.

1. I seriously doubt it's a thermo joke. I just don't see that being The Giant's style.

2. never mind. I'm not going into the technical issues with the above...