These fruits of the Osage Orange Tree are nicknamed "Monkey Brains". I found them under a grove of trees near Black Rock Lighthouse in Bridgeport while geocaching.
I had never run across this bizarre tree before, so I looked it up on Wikipedia and discovered more interesting tidbits about it. Although the fruit are not very toxic, they tend to make you vomit. An oil of the fruit shows promise as a mosquito repellent.
Also, there are no animal that eat the fruit, so what's the point? Fruit is normally designed to be eaten for seed dispersal. According to one theory, giant ground sloths used to eat it, but went extinct when people came to North America.
The tree is native to the Arkansas, Oklahoma and Texas and is also called Osage Apple, Wild Orange, Mock Orange and Bodark. The fruit has other nicknames besides Monkey Brains, including Monkey Ball, Monkey Fruit, and Brain Ball. So there you go, learning something every day.
By the way, the lighthouse and Seaside park are very picturesque and easy to get to in the middle of the winter. No crowds. The lighthouse was once on a island, but that's been connected to the mainland by a huge causeway of boulders you can walk on. From the parking lot, it's about a 15 minute walk.