Cats love peanuts, playing with them I mean. As I write this, my boys are running through the house with our two kittens, throwing peanuts and watching the cats go nuts over them. The kittens pounce on them, pick them up and guard them with their paws, then wait for you to throw them again.
When you think about it, what’s not to like? Peanuts are small, light, rattle when they move, are cheap and non-toxic, all good qualities for a cat toy. I think the best ones are the small roundish ones with a single nut inside. These are the most like a ball and skitter “realistically” when thrown or kicked by a cat.
Update: Emma, the wilder of the two kittens, ate a few of the peanuts. I looked it up and peanuts are not toxic to cats. In my thirty plus years of experience with cats, I’ve found that most cats tolerate non-meat foods pretty well, depending on their youthful environment. My 14 year old cat Buster was homeless for his first two years and lived off various junk. The rescue group said they captured Buster in a nursing home taking food from the residents there. He eats just about anything a person would, as long as it’s not spicy. He eats cat food like our other cats, of course. He just doesn’t limit himself to that.