In Chinese (probably Mandarin) it's called an Erhu. D's family just calls it a two-string.

As you can see, the bow is attached between the two strings (ie, unremovable). Sound is created by drawing the bow across the strings, just like a violin. Different pitches are produced by holding the strings down in specific areas, just like a violin or guitar.

Unlike a violin, it sounds like a cat being killed.