def parse_factor_polarity_curation(cur):
    """Parse details from a curation that changes an event's polarity."""
    bef_subj = cur['before']['subj']
    bef_obj = cur['before']['obj']
    aft_subj = cur['after']['subj']
    aft_obj = cur['after']['obj']

    if bef_subj['polarity'] != aft_subj['polarity']:
        return 'subj', aft_subj['polarity']
    elif bef_obj['polarity'] != aft_obj['polarity']:
        return 'obj', aft_obj['polarity']
    else:
        return None, None