Zi Collection, Page Position: Lower Radical: Mouth (kǒu) Page 180, Entry 05 In the Book of Rhymes (Guangyun) and the Collection of Rhymes (Jiyun), the pronunciation is given as ao (level tone), which is the same as the sound of ao (falling-rising tone). The Jade Compendium (Yupian) defines it as a licentious sound. Additionally, the Collection of Rhymes (Jiyun) records the term ao za, which refers to the noisy barking of dogs.