This hopping frog is from Fay's book, "LEGO MINDSTORMS NXT Z00".
Can you see what Fay has done to make the frog jump and give it forward propulsion? Can you also see what gives it stability and traction? (The frog can be made from one retail kit and a couple of inexpensive, non-LEGO parts).
(P.S. The small human on the left is our son).