Plop is a Ceratophrys Cranwelli. Check the frogs thumb on each hand. If the frog is a male it will have dark spots in the center of the thumb facing towards the frogs chest. They will look like a mole. These are called nuptial pads and are used by the males to hold onto the females during Amplexus. Also male frogs will begin to call(croak) as early as 5.5 months of age. You could go on YouTube and look up Pacman Frog Mating calls and play them. Usually this will stimulate a male frog to begin calling if he is mature enough to do so.