I cooked some poultry stuffing and left it in a bowl in the fridge overnight covered with aluminium foil. In the morning there were holes in the foil where it had touched the stuffing, which was stained black under each hole. Uncooked stuffing does not produce this effect, and it makes no difference whether the stuffing is cooked inside the bird or separately. What is going on here? And is the black stain poisonous?
Andrew Stiller, Philadelphia, Pennsylvania, US