What makes these sea horses so silly? Well, aside from the great jokes, animated role play, and an array of party tricks, your sea horses will actually grow in water. That's right, you read right, they grow in water! Play hide and go seek or catch with them once they are fully hydrated. Or not. Anyway, they grow and will retain their impressive stature for at least a week before shriveling to their pre-hydrated state. Store them in a sealed plastic bag, and use them again.