parabens! It took my 7 tries, but 2 of those were me thinking I could make the frogs jump both directions. I was thinking it would be a hannoi tower sort of thing and move one forwards, then all back, then one more and so on. Obviously not.
first try... sadly, a few years ago we did a team building thing at work and they did this exact same thing. Except we all played the part of the frogs!