If you're a butterfly enthusiast like I am, you have probably heard of the butterflies known as "crackers" in the genus Hamadryas. These interesting leps produce a cracking sound via swollen veins in the forewings which strike one another if the male forces the wing upstroke to maximum amplitude. The females lack this sound-producing mechanism. A gentleman living in the Rio Grande Valley posted a really neat video of a Guatemalan Cracker in his yard making this cracking noise. I have never seen it in person, but it's quite a sight to see on the video. I've been told that the video features a particularly agitated individual. The cracks are usually not as frequent as seen in the video. Enjoy!