The answer is Pandora's box
Step-by-step explanation:
Pandora's box is a mythical object that in Ancient Greece was believed to release disease, problems, and death when opened. This object is mentioned by the mother of Harper to tell the father the curiosity and questions of Harper might be the beginning of problems. Moreover, when the mother mentions this mythical object she is making an allusion, which means she mentions or refers to an external idea, in this case, she refers to a Greek myth and the mythical object in it.