Daily Questions About the Metallic Arts; Day 18

Highly unethical mad science question about the fourth metallic art. For the sake of argument, let us say that I don't kill the subject. What happens to a Singer's form, if anything, once its heart is in a metal cage? It wouldn't act like a Fabrial I would assume, due to them not reacting to Spren in the same manner that a normal Fabrial does, but by being a similar principle, I also assume that *something* would happen.

Day 17
Day 19