Here's a great way to take a "normal" dog toy and turn it into a discrete toy for your playroom. Whether you're into pup play or not, anyone into BDSM can get a lot of use out of this one. This idea will work for CBT or TT.
As always, make sure bdsm/kink play is safe, sane, and consensual. Never leave your sub alone during bdsm play. Especially with CBT, it’s important to test devices on yourself first before using them on your sub. You can’t be a very good Dom if you have no idea what it feels like. Chances are you’ll either go too extreme or bore your sub to tears. Actually either extreme of that spectrum could have your sub in tears, whether through pain or boredom. Always keep one very important rule in mind when planning and participating in a session: If you break your sub, you don’t get a new one! ;)
Find a way to tie the thin piece of rope or string to the Bumble Ball. There is usually a small slot in the area of where the two halves come together. If not, you can probably tie it around the base of one of the nubs as there are usually small gaps there. Once that is tied, tie an extra loop in the remaining part of the rope/string so you can tie another piece of rope the the loop.
Get your sub restrained in your favorite position (keeping this idea in mind) with space under his balls (or even under his nipples, see Alternative options #1). For the balls, you'll want to make sure his legs are spread and tied off. But there are many possibilites with this one, so experiment with it and find what you like best. As a Dom, you don't necessarily need to tie your own balls to get a feel for how this will work with your sub (although that's the best way to know). You can simply hold a rope in that general area to see how the Bumble Ball moves in that scenario.
Tie the other piece of rope around the base of your sub's balls (or dick/balls together, or to a parachute ball stretcher or similar device), and tie the other end of the rope to the string attached to the Bumble Ball. You'll want to leave some slack in most cases to allow the ball some room for movement, but not a lot of slack. After getting your sub in position, I'd say make the rope taut from balls to the ball, then add another 6-12" of slack and tie it off.
Turn the Bumble Ball on.
Kick back and watch the show as the ball vibrates and bounces around on the floor. When it reaches the end of the rope slack, it will tug on your sub's balls. Then it might bounce back, or it might keep trying to get away, tugging on his balls more. Part of the fun here is it's pretty random.
Have fun watching the ball roll around on the floor, as it tugs your sub's tied balls with almost every movement.
Instead of using this idea to tug on your sub's balls (or in addition to), you can use it to tug on his clamped nipples. For the nipples, it's best if you have him leaning forward (see photos). Then add nipple clamps or clover clamps (warning, these are pretty intense!). Then tie the rope from the chain that connects the nipple clamps to the Bumble Ball.
Or use a nipple clamps to cock ring set so the Bumble Ball tugs on both the sub's balls and nipples when it gets too far away.