Several years ago, took my kids to the National Zoo. As we were walking around we heard this very loud, slow repetitive grunting off in the distance. Didn’t sound like any sound I’d ever heard an animal make. Started walking around until we saw a small crowd gathered around an enclosure where the sounds were coming from. Managed to get close enough to see what was happening. Turns out it was a pair of Galapagos tortoises making baby tortoises. It was probably one of the 5 loudest sounds I’ve heard an animal make. The best part was when one of my kids asked what the tortoises were doing and my wife came up with the inspired response, “They’re playing a game of leapfrog.”