def combine_words(word1, word2):
    """Combines two words.  If the first word ends with a vowel and the initial
    letter of the second word is only consonant, it merges them into one
    letter::

    >>> combine_words(u'다', u'ㄺ')
    닭
    >>> combine_words(u'가오', u'ㄴ누리')
    가온누리

    """
    if word1 and word2 and is_consonant(word2[0]):
        onset, nucleus, coda = split_phonemes(word1[-1])
        if not coda:
            glue = join_phonemes(onset, nucleus, word2[0])
            return word1[:-1] + glue + word2[1:]
    return word1 + word2