Sounds are syllables + tones

def _sounds_re(include_erhua=False):
    """Sounds are syllables + tones"""

    tone = '[1-5]'
    optional_final_erhua = '|r\\b' if include_erhua else ''
    pattern = '({}{}{})'.format(_joined_syllables_re(), tone, optional_final_erhua)
    return re.compile(pattern, re.IGNORECASE)