def almost_same(this_word, next_word):
    """Return true if two words are exactly one character different"""

    different = False  # we haven't found any differences yet
    for i in range(len(this_word)):
        if this_word[i] != next_word[i]:
            if different:
                # we were already different, now we are too different
                return False
            else:
                # we are just different enough
                different = True

    return different