Walk over to Otis the black-and-white cow. He's standing by the red tractor. He will ask you to squirt six animals. Take the sunglasses out of your inventory and take note of the milk cartons. Running into these will refill five milk squirts. Since you have five squirts and you need to squirt six animals, you will need to fill up at least once. Using the target lock will narrow in on the animals, making it easier to squirt them. Once you have squirted six animals, return to Otis.