My belly button

My belly button has been the most fascinating thing to me. First off, my innie belly button has turned brown, and has become extremely rubbery, and squishy, and is becoming more and more shallow. It's now also doing tricks! When I cough or laugh really hard, it POPS! like a turkey thermometer then goes back in. Last night I was coughing after drinking something and it going down the wrong pipe, and I was holding my stomach with my hand, and the POP! scared the crap out of me, and made me laugh hysterically. I didn't know my belly button could do that!