One of my player's is curious about how weapon finesse applies to his weasel familiar, which deals 1d3–4 plus attach melee damage. The decrease is due to the weasel having a strength ability score of 3.
The weasel also has the weapon finesse feat, which allows it to swap its strength modifier with its dexterity modifier for light weapons (including natural weapons). The weasel has a dexterity of 15, so attacking with dexterity rather than strength would result in a +1 rather than the -4.
Am I missing something, or is this correct? Or is it simply something left for the DM to decide?