Passage Summary: Rhett thinks he should get a free ride because his friend is going that way anyway, but Barbara thinks that's like stealing heat from a neighbor's room just because they aren't using it.

Reasoning: Rhett argues he shouldn't pay for gas because his presence doesn't increase the driver's costs; Barbara uses an analogy about diverted heat to suggest this logic is absurd.

Analysis: To find the point at issue, we apply the 'Agree/Disagree' test to the underlying principle of Rhett's argument. Rhett believes that if a service or resource is provided at zero marginal cost to the provider, the recipient has no obligation to pay for it. Barbara's analogy of the 'unused spare room' is designed to show that Rhett's logic leads to ridiculous conclusions, implying she rejects his premise. The disagreement centers on whether the lack of additional expense for the provider justifies the recipient's refusal to pay.