What is the name of this tree in NW Alabama?

We were traveling through NW Alabama, stopped at a rest area, and as I was walking my dog, I noticed these cool looking little brown balls with holes in them and spikes all around...they were neat looking so i gathered about a dozen to display in my home in a centerpiece arrangement....but, I want to know if these little circular balls that are on the same level as a pinecone are safe to have in the house, and what they are? THANKS!