What does "anal violin" mean in gay sex?

What is anal violin?

An ancient sex toy, that simulated the playing of a violin.

Definition

The use, in ancient culture, was where a piece of cat gut (violin string) is attached, affixed, to a round object, such as a ball.  Wood, plastic, or Ivory can be used. (Plastic being a more modern material for use)

This contraption is used as a anal toy and inserted into the anus, then tightened or made taut. Usually the inner muscles are contracted, to make the string taut, to suck in the ball, and hold it.

Once taut, a violin bow is used to 'play' the string, which vibrates inside the rectum, stimulating the insides giving sexual pleasure to the recipient.

Noteworthy: Considered to be a popular 'toy' of the Eunuchs of the Ottoman Empire.