Hyacinth knows exactly how to use the spell to unlock hidden secrets, but she'll only tell it to creatures who can be trusted and won't take advantage of the trust in a malicious way. She makes sure nobody uses the pond's magic to harm themselves or others in any way.
You may be wondering: can she see? Technically, she can see, but only through her mental "third eye". Her real eyes are covered to avoid being affected by hypnosis, optical illusions, and also the appearance of a creature.
