Just by looking for two quick clues, you can tell that this is a green frog (Lithobates clamitans), and a female. Do you see those two long ridges running along its back? Green frogs have them, and bullfrogs don’t. To sex this frog, check out the circle behind its eye. In males, this hearing organ, called a tympanum, is huge, but in females it’s only about as large as the bulging eye itself.