If by rattlesnake-looking things you mean the bracts (the part left after the flower falls off), the seeds would be deep in the bottom of the inside. Being a mint-relative, there would be (up to) four tiny black (almost-) spheres inside. They they aren't black, they aren't ready. All you would need to do is carefully cut off the stems with the rattlesnake thingies on, turn it upside down on a piece of cloth or paper, and carefully squeeze the rattlesnake thingy from the bottom outward, and the seeds should drop out, if they don't by gravity already. Good luck...