Wikipedia
Zhuihu
The zhuihu (坠胡, pinyin: zhùihú; also called zhuiqin or zhuizixian) is a two-stringed bowed string instrument from China. In construction, it resembles the sanxian, and likely evolved as a bowed version of that musical instrument. Unlike bowed string instruments in the huqin family (such as the erhu), the zhuihu has a fretless fingerboard against which the strings are pressed while playing.
The zhuihu is used to accompany a form of traditional narrative singing referred to as zhuizi, which originated in the Henan province of China. A more modern version of the zhuihu called the leiqin was developed in China in the 20th century. Another related instrument is the Japanese kokyū.