HA! Mom used to get this. I remember cutting them open to get the big plastic ball out of them after they were used up. You could get balls out of all the roll-on deodorants back then.
You couldn't do much with them. I remember we used to send them crashing into each other down Hot Wheels tracks. We tried playing marbles with some one time, but they were too irregular & light. Mostly we threw them against brick walls until they shattered.
It was the 1970s. We didn't have the Internet, okay?
My childhood bestie was the son of the local mortician. I kept noticing he had these unusual yellow rubber balls with a slight convex indent on one side, and I asked one day what they were.
"Replacements for when they take the eyes out for transplant," he said.
For corpses that still have their eyes, there are tiny little cups to put over them. The outside surfaces of the cups are covered with tiny little spikes.
They perform the dual purpose of preventing the eyes from looking sunken & keeping the eyelids shut.