def list_to_once_words(word_list: list):
    """
    returns a list of words that appeared _twice_

    :param word_list:
    :return: list of words that appeared twice
    """
    capitalized_word_list = [w.upper() for w in word_list]
    unique_words = set(capitalized_word_list)
    word_frequency = {w: capitalized_word_list.count(w) for w in unique_words}
    words_appear_twice = [k for k, v in word_frequency.items() if v == 2]

    return words_appear_twice