Broad Rimes (Guangyun) uses the pronunciation constructed from the sounds of xin and yu; Collected Rimes (Jiyun) uses the pronunciation constructed from the sounds of xue and lv. Pronounced xu (falling tone). The Jade Chapters (Yupian) defines it as the appearance of blowing through the mouth. Broad Rimes (Guangyun) describes it as the sound produced by the mouth, like xu xu. Collected Rimes (Jiyun) defines it as a sound. Sometimes also written in a variant form (xu). Additionally, Collected Rimes (Jiyun) provides a pronunciation constructed from the sounds of chun and yu. Pronounced shu (falling tone). It is the sound used to drive a dog.