A woman walking with a boy is asked by another woman about their relationship.…

In blood-relation puzzles, a relational identity clue ("X and Y are the same person") should first be checked against the SIMPLEST possible family arrangement — does the equality hold automatically once the two people in question are assumed to be directly related — before reaching for a more roundabout, multi-generation construction.

1. Let U be the woman's maternal uncle — her mother's brother.

2. Suppose the woman IS the boy's mother. Then the boy's maternal uncle is the brother of the boy's mother — that is, the woman's own brother; call him X.

3. Since X is the woman's own brother, X shares the same mother as the woman does.

4. So X's own maternal uncle (his mother's brother) is exactly U — the same person as the woman's maternal uncle.

5. This means "the woman's maternal uncle" and "the uncle of the boy's maternal uncle" are automatically the same person (U) whenever the woman is the boy's mother — exactly the condition the statement describes, with no further coincidence required.

Now weigh the other labels. A maternal aunt (a sister of the boy's mother) would in fact satisfy this very same identity — but only if the boy's mother actually has such a sister, an additional person the statement never introduces; the clue on its own does not require her to exist. A grandmother–grandson link would need the woman to sit two whole generations above the boy, which the single-generation structure of the clue rules out. The mother–son reading is the only one that satisfies the equality with no extra, unstated family member, so that is the relationship the statement fixes.

So the woman is the boy's mother, and the correct answer is "Mother and Son."