If humanity were to create an ultra-intelligent computer then humans would be far surpassed. This part of the passage says that because our minds would be so simple compared to that of the machines at the point of the singularity that we would be little more than rabbits. This idea is astounding because our mental capabilities are vastly superior to those of rabbits or other animals and the idea that we could be so easily surpassed and so greatly surpassed is probably terrifying to many people. This is probably what makes the idea of a singularity such an abstract idea.