It appears to be a gord (spelling?) that are caused by something blocking the tubes in a plant causing it to grow like a tumor. They can sometimes contain insects.

It'd help to know the size of it.

Off hand, it could be an old peanut buried by the local squirrel. LOL

Have you tried to cut into it or break it open?

https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-xpf1/t1.0-9/10376002_10204207980745179_4514144704115853075_n.jpg