A poison ring is a ring that has a tiny container or compartment inside of it that can hold various substances, typically poisons. The purpose of the ring was to secretly carry poison and then discreetly administer it to someone without anyone else knowing. The ring can be opened by a tiny latch or mechanism and the poison can be actually stored in the ring.
But it is important to remember that these rings are not just for playing with. Poison can be very dangerous and cause harm to someone's body if it is not used properly. There are many stories and legends about people who used poison rings to harm others, which is not okay. It is important to always use things like rings for good and kind purposes and never to harm others.