The idea of 'underground' holds strong resonance for humans, with connotations of being the entrance to the 'underworld', being secret or hidden. Underground can even include connotations of the revolutionary or disrespectable: exactly the connotations of the witch word we apply to ourselves.
The placement of an object also has a strong resonance in some old -school magic. As a priest of Hecate I'm well used to leaving things at crossroads and in graveyards. In this instance the object has been left in an underpass, thus leaving the person it represents at the mercy of the underworld.
Zippy has been given to two degus to chew. For creatures who will normally eat anything they took an instant dislike to her (sensible chaps). They did chew her zip and eyes, but otherwise she has been lying on the bottom of the cage being soaked in urine and with faeces landing in her mouth periodically. I'm informed that the smell of urine will attract rather than repel the rodent denizens of the underworld, who will hopefully take her stuffing to make beds with. To encourage this she has been opened up and tasty rat treats stuffed in her. She has then been left in a pool of urine in an underpass for...who/whatever to find.
Bye bye Zippy.