Aspiration prior to injection is done to ensure that:
O
the needle is not in the dermal layer
O
the needle is not clogged
O
blood vessels have not been pierced
O
blood vessels have been pierced

answer: no, they are not.*

although rubber bands that contain excessive amounts of dye, toxins, or additives are sometimes toxic, most rubber bands do not cause any health issues. since they are typically made of latex, (a natural substance that is extracted from trees) they are not dangerous in any way if you chew them or accidentally ingest a piece of rubber band. however, chewing rubber bands does pose a choking hazard and is not a good habit to have.

*depending on the type of rubber band. the typical rubber bands that you see at stores are not toxic, but other types of rubber or latex that contains certain chemicals may be unhealthy and hazardous.