Eastern black nightshade.
Seedlings:
Leaves always seem to have insect feeding holes on them (below):
Mature plants:
White flowers (left) and dark (poisonous) berries with seeds inside (right):
Mature plants with berries (below):
Bitter nightshade:
Leaves:
Mature plant:
Mature plants with berries (poisonous) (left, center) and purple flowers (right):
