Some are even filled with fine powder surrounded by a rubber membrane.
The sound is actually very relaxing.
Just a second mini-break could be all you need.
Place two Chinese medicine balls in the palm of one hand.
Or, try to see how many times you can toss a stress ball back and forth before someone drops it.
Hand Strengthening Exercises HealthGuidance:
This is the reason why a lot of people keep stress balls in their desk at the office.
I find juggling therapeutic, it's easier to do then most people think and can be learned from books.