You know, I've actually seen that in the wild before. Most frogs have a distress call that they issue when they feel threatened. Bullfrogs and Green frogs often let out a quick squeak when they are startled and jump into the water. If you've ever seen a frog being eaten by a snake you'll know that frogs can make really weird noises. On one occasion I caught a Bullfrog and the moment it was picked up it just started screaming. I swear that thing could scream this high pitch AIIIIIIIIIIIIIIIIIIIIIIIIII for at least 15 straight seconds. Much like the squeak as they jump into the water, it is a distress call either to confuse a predator or to warn nearby frogs that danger is near