Animal, vegetable or mineral?

This strange object, a dense, wrinkled green globe about 5 inches in diameter, I found lying under the trees in Bartram's Garden, an 18th century estate in Philadelphia which is now a historic site with the wooded grounds beside the Skuylkill River that are botanist's paradise.
I carried the object with me until I found someone who could tell me it was called an Osage Orange, the fruit of the Osage Orange tree. It has other names too: horse apple, monkeyball and brainfruit. It's not related to the oranges but to the mulberry. It's composed of many tiny seeds, much loved by squirrels, and it has the reputation of deterring spiders and insects if kept around the house.
The Bartrams, father and son, were America's first botanists, responsible for collecting and naming the plants of the New World according to the Linnaean system so I was pleased to discover a botanical something that was new to me in their own garden.

More about the Osage Orange here.