Passage Summary: Some people think a special kind of hot gas causes ball lightning. The professor says if that were true, the lightning would be bright and go up. Since the lightning the professor saw was dim and moved sideways, the professor concludes that hot gas is never the cause.

Conclusion: Superheated plasma with failed electrical resistance is never the cause of ball lightning.

Reasoning: If plasma were the cause, ball lightning would be bright and rise, but the professor's specific observations showed dim lightning that moved horizontally.

Analysis: The professor is making a huge leap from "the ones I saw didn't act like plasma" to "plasma is never the cause." To make this logically sound, we need to bridge the gap between the professor's specific observations and all instances of ball lightning. Look for an assumption that suggests the professor's observations are representative of all ball lightning, or that if plasma were a factor in any ball lightning, it would have to be a factor in all of them.