Tanaka Tadayoshi's Iron Snake

Origin
It's not uncommon for metal workers and artists to create small but impressive works simply to show off their skill. That's what obscure Japanses artist Tanaka Tadayoshi did when he crafted this small yet perfectly articulated wrought iron snake.

At some point, his creative passion infused into the metal, and the artifact was born.

Effects
Normally dormant, this artifact doesn't activate until it come into contact with body heat. Like a real reptile, without an external source of warmth, the snake cannot move at all. Also live a real reptile, when active the snake will attack anyone who disturbs it. Unfortunately if you're close enough to activate it, you're close enough to disturb it and one might discover the artifacts unusual brand of 'venom'.

When bitten, the victims blood slowly transmutes into liquid iron, which quickly cools in the body. This process is extremely painful and takes some time, and the result is a perfect iron ma of the human circulatory system. And one dead human who it belonged to, of course. The process is reversable by neutralizing the artifact before death occurs, which tends to be when the iron reaches the heart of brain.