Re: Mouse balls.
There used to be these small plastic spheres about the size of a marble. The plastic was clear, there was clear liquid inside, & a smaller sphere inside floating in the liquid. Some places sell things of that design with the inner sphere being a compass for navigation. The toy was a "floating eyeball". I used to have fun swapping the mouse ball for an "eyeball" & wedging it in place so the mouse wouldn't track. The owner would flip it over to check for gunk, see the eyeball looking back at them, scream & throw the mouse away as they scrambled from their desk chair like their ass was on fire. I'd "go check what was wrong", replace the eye with the ball, & feign innocence when the person returned gibbering about eyeballs.
I'm not evil, I prefer the term "creatively vindictive". ;-D