Validates a french catch phrase.

        :param catch_phrase: The catch phrase to validate.

def _is_catch_phrase_valid(self, catch_phrase):
        """
        Validates a french catch phrase.

        :param catch_phrase: The catch phrase to validate.
        """
        for word in self.words_which_should_not_appear_twice:
            # Fastest way to check if a piece of word does not appear twice.
            begin_pos = catch_phrase.find(word)
            end_pos = catch_phrase.find(word, begin_pos + 1)

            if begin_pos != -1 and begin_pos != end_pos:
                return False

        return True