What is best demonstrated by unsterilized body piercing tools?

Unsterilized body piercing tools best demonstrate a common risk of HIV transmission because they can carry blood from one person to another. When shared or reused without proper sterilization, these tools can introduce the virus into an individual's bloodstream, especially if they cause breaks in the skin or if blood from an infected person comes into contact with the next person's open wound.

This scenario highlights how activities involving blood exposure, such as body piercing, present significant risks for the transmission of HIV and other blood-borne pathogens. Proper hygiene and sterilization protocols are crucial in environments like tattoo parlors and piercing studios to prevent such risks, emphasizing the importance of using sterile equipment for any procedure that could involve blood.