AbigailII:  Interestingly, if you know there are two frogs in four squares, you shouldn't guess.  However, if you know there are two frogs in five squares, you should guess. 

In both cases, you'll guess right often enough that you'll score more points for the right guesses than you'll lose for the wrong guesses.  However, with four squares, if you guess wrong, your opponent can guess with a 2/3 chance of being right, which is good enough that the points he gets from guessing right outweighs the points you might get from guessing right.  With five squares, you still leave your opponent with enough options that guessing is a bad idea, so you just get the payoff from your initial guess.