As far as I'm aware, not legal to bring across the border, same as the gall bladder.
It appears I may have been wrong about this. Perhaps someone can confirm this either way?
Steve, you are correct. Swizzle stick is considered an organ. A guy I was with in 2015 attempted to bring one back. First and most often asked question at Customs is if you have a bear penis. The guy I was with admitted to having one. Almost 2 hours later and a lot of paperwork, we were on our way.
We have been grilled by CBP in subsequent trips (2017 and 2019) if we were bringing a bear penis back which we weren't. Best part of the whole 2019 "interrogation" was the officer was clearly embarrassed to say bear penis in front of my daughter. He called it every other name under the sun!