This expansion connects to the mouse port and gives you two Amiga style mouse ports for use with mice or joysticks.

Unlike other mouse port adapters this one fits to the outside and does (Did) not affect the warranty.

The Brick-ette mouse port adapter was made by Expansion Systems in 1993 and when new this little device cost £39.99 in 1993.

If you can not tell, it connects with a wire coming out the side.
It is made of metal affect plastic with a small PCB with a chip doing the hard work.
There are a few of these around as most people sold these when new.
Try looking at oldsoftware.com for one.

Most joysticks are black so they look great with the CDTV and Amiga made a black standard mouse for Amigas.

This makes adding a joystick to the CDTV easy but a little expensive.
Other options include the trackerball and the Das Vector.