Changeling blood from floors and gibs doesn't react to heat.

[Isaacs Alter Ego]

While I can see the validity of using the blood that a changeling sheds for this purpose, a gibbed changeling is uh... well if you gibbed it and you weren't absolutely sure it was a changeling before you did it, you have bigger things to worry about than whether it was an alien or not.

The situation in question that brought this up was another player crushering another, which I witnessed, but had not witnessed the crushed player doing anything changeling like. So I tried to investigate in order to confirm it was a good player killing a ling, and not just a traitor killing someone and using a cover story. The blood didn't react, though, even though the person was confirmed as a changeling through other means. So it can affect a round even when everybody's playing nice with the rules.