Question

Tonight, while picking mustang grapes I spotted something growing along a fenceline that I can't identify.  It looks like a smooth-skinned lime but it is soft.  When opened, it is mostly hollow inside with a white spongy lining and alot of seeds down the middle.  I don't think it's edible as I took a small taste and it tasted like slightly sweet styrofoam.  I live in East Texas and have never seen this before.  I'll try to post a picture tomorrow if no one has any ideas.   A Google search didn't reveal anything that looks like this..